The European athecate hydroids and their medusae (Hydrozoa, Cnidaria): Filifera Part 4

Abstract

The European athecate hydroids and their medusae (Hydrozoa, Cnidaria): Filifera Part 4. - This study reviews all European hydroids belonging to the filiferan family Eudendriidae. Two new species occurring in the northeastern Atlantic are described: Eudendrium. capillaroides new spec. and Eudendrium unispirum new Spec. Eudendrium vaginatum Allman, 1863, is redescribed. It is characterized by a special type of nematocysts and traits of the perisarc. It is distinct from Eudendrium annulatum Norman, 1864, which is a separate, valid species. Eudendrium fragile Motz-Kossowska, 1905 and Eudendrium islandicum Schuchert, 2000 are both recognized as synonyms of E. album Nutting, 1898. Eudendrium stratum Bonnevie, 1898 and E. plantum Bonnevie, 1898 are both recognized as synonyms of E. rameum (Pallas, 1766). Eudendrium insigne Hincks, 1861 is indistinguishable from E. ramosum and newly collected material from the type locality confirmed this. Eudendrium insigne must thus be regarded as a synonym of E. ramosum (Li

Full text

The European athecate hydroids and their medusae
(Hydrozoa, Cnidaria): Filifera Part 4
Peter SCHUCHERT
Muséum d'histoire naturelle, CP 6434, CH-1211 Genève 6, Switzerland.
E-mail: Peter.Schuchert@ville-ge.ch
The European athecate hydroids and their medusae (Hydrozoa,
Cnidaria): Filifera Part 4. - This study reviews all European hydroids
belonging to the filiferan family Eudendriidae. Two new species occurring
in the northeastern Atlantic are described: Eudendrium capillaroides new
spec. and Eudendrium unispirum new spec. Eudendrium vaginatumAllman,
1863, is redescribed. It is characterized by a special type of nematocysts and
traits of the perisarc. It is distinct from Eudendrium annulatum Norman,
1864, which is a separate, valid species. Eudendrium fragile Motz-
Kossowska, 1905 and Eudendrium islandicum Schuchert, 2000 are both
recognized as synonyms of E. album Nutting, 1898. Eudendrium stratum
Bonnevie, 1898 and E. planum Bonnevie, 1898 are both recognized as
synonyms of E. rameum (Pallas, 1766). Eudendrium insigne Hincks, 1861
is indistinguishable from E. ramosum and newly collected material from the
type locality confirmed this. Eudendrium insigne must thus be regarded as
a synonym of E. ramosum (Linnaeus, 1758). A re-examination of the type
material of Eudendrium elsaeoswaldae Stechow, 1921 revealed that it is
conspecific with E. ramosum (Linnaeus, 1758), becoming thus a new
synonym of the latter.
Perigonimus multicornis Allman, 1876 is indistinguishable from Myrio -
nema hargitti (Congdon, 1906) and must be regarded as a senior synonym
of the latter. Because it seems likely that the original type locality
designation “Kattegat” was incorrect, it should not replace M. hargitti or M.
amboinense.
Keywords: Cnidaria - marine - Hydrozoa – Eudendriidae - revision - taxo-
nomy - north-eastern Atlantic - Mediterranean.
INTRODUCTION
This study is the fifth in a series of taxonomic revisions and reviews of the
European Anthoathecata (=Anthomedusae, Athecata). The previous ones are:
Schuchert (2004; Oceaniidae and Pachycordylidae), Schuchert (2006; Acaulidae,
Boreohydridae, Candelabridae, Cladocorynidae, Cladonematidae, Margelopsidae,
Pennariidae, Protohydridae, Tricyclusidae), Schuchert (2007; Bougainvilliidae,
Cytaeididae, Rathkeidae, and Pandeidae), Schuchert (2008; Hydractiniidae, Rhysiidae,
Stylasteridae). The current paper treats one family only, namely the Eudendriidae.
Many of the European Eudendriidae have recently been studied by Marques et al.
REVUE SUISSE DE ZOOLOGIE 115 (4): 677-757; décembre 2008
Manuscript accepted 23.06.2008

(2000a, 2000b), but an update and more complete species descriptions, including also
all species of the northeastern Atlantic, was needed. Although the members of the
genus Eudendrium are rather unique and it is easy to identify a hydroid as belonging
to this genus (Fig. 1), the identification at the species level is sometimes rather diffi-
cult. As outlined by Marques et al. (2000b), the state of the Eudendrium species was
confused until the middle of the last century, with many species being unrecognizable.
The application of nematocyst data improved the situation considerably and nowadays
species identification relies predominantly on the cnidome. This change in taxonomic
practice made most previous species records untrustworthy. Other morphological
characters are still important, though, especially in those species that have the same
type of capsules (e. g. E. ramosum, E. rameum, E. merulum etc.). It seems, however,
that the species diversity has been underestimated.
Concomitantly with this study, also a comparison of the 16S gene DNA se-
quence was begun, using besides the species and populations mentioned here many
more from various places all over the world. Preliminary results of this study, which
will be published elsewhere, indicate that several morphospecies of Eudendrium are
actually composed of more than one lineage and thus likely belong to different species.
Moura et al. (2008) arrived at a similar conclusion.
MATERIAL AND METHODS
See also Schuchert (2008). Where possible, it was attempted to supplement the
species descriptions by sequence information of part of the 16S mitochondrial rRNA
gene. The methods to obtain DNA sequences are described in Schuchert (2005, 2007).
All sequences have been submitted to the EMBL database (accession numbers
AM991292-AM991307). The origin and identity of the material used to obtain the 16S
sequence data as well as the accession numbers are given for each species in the section
"Material examined". 16S sequences of some non-European Eudendriidae were also
determined, namely Myrionema amboinense (MHNG INVE60162, aquarium culture
of unknown origin, AM991292), Eudendrium maorianus (MHNG INVE29972, New
Zealand, AM991303), E. ritchiei (MHNG INVE29971, New Zealand, AM991304).
All available sequences, including also those published by Moura et al. (2008), were
used to visualize the relatedness by a Maximum Likelihood analysis of HKY distances
using the program PHYML described by Guindon & Gascuel (2003). A bootstrap
analysis using 100 pseudoreplicates was made.
ABBREVIATIONS
BELUM Ulster Museum, Belfast, Northern Ireland
BMNH The Natural History Museum, London, England
ERMS European Register of Marine Species (Costello et al., 2001)
MHNG Muséum d'histoire naturelle de Genève, Switzerland
ICZN International Code of Zoological Nomenclature
IRSN Institut Royal des Sciences Naturelles de Belgique, Bruxelles
SMNH Swedish Museum of Natural History, Stockholm, Sweden
ZMO Zological Museum of Oslo, Norway
ZMUC Zoological Museum Copenhagen, Denmark
ZSM Zoologische Staatssammlung, Munich, Germany
r ratio of nematocyst capsule length and width
s ratio of shaft and capsule length in discharged capsules
P. SCHUCHERT
678

GENERAL MORPHOLOGY AND IMPORTANT FEATURES
Eudendrium colonies are anchored to the substratum by tubular stolons. The
stem of the colony may be branched or unbranched (=stolonal), either monosiphonic
or polysiphonic (=fascicled, composed of several tubes). The stems and pedicels are
always covered with firm perisarc which becomes abruptly very thin and filmy below
the hydranths. The perisarc of the thicker tubules is usually smooth or wrinkled with
characteristic groups of annulations at the origin of branches and sometimes also
elsewhere.
The hydranths are relatively large for colonial marine hydroids and distin -
guished from all other families of the athecate hydroids by a wide, trumpet-shaped or
spherical hypostome. The tentacles are filiform, their nematocysts often in transverse
linear arrays, the density decreasing towards proximal. The nematocysts can be either
oriented parallel to the tentacle resulting in rather smooth tentacles, or they can be
inserted obliquely giving a spiny appearance (Puce et al., 2005). On the hydranth body,
there can be a band or buttons of nematocysts (Figs 1A; 3B). Rarely, there is also a
tentacle-like protrusion near the base of the body, a nematophore (Fig. 1A). Near the
base of the hydranth column, sometimes also in the middle, there is always a ring of
specialized cells that secrete the perisarc in a fold of the epidermis. This basal groove
is always present, but in some species or under some circumstances it can become
rather inconspicuous or almost invisible.
Male and female gonophores are normally produced in separate colonies, but a
few species are hermaphrodites (e. g. E. simplex). Reproduction is by fixed sporosacs
which in many cases develop in a whorl round the base of the hydranth. The hydranth
bearing the gonophores can be fully formed or reduced to various extents and is then
called a blastostyle. The development of the gonophores starts concomitantly with the
development of the budding of the new hydranth (blastostyle), even before the
tentacles develop (Fig. 16C-E). In some species the hydranth grows to the same size as
of a non-reproductive polyp, in others the hydranth development stops and often it gets
atrophied again (e. g. Fig. 34E-G). There is considerable variation of this process
between the species and to some extent it could also depend on the environment. In
some species the gonophores/sporosacs form without a trace of a hydranth, the gono-
phores issuing in a tuft from the end of a pedicel. It is thus important to bear in mind
that the blastostyles can change form and size during development, which makes it
sometimes difficult in preserved material to decide whether they are actually reduced
or only in an early stage of development, this in particular also for female gonophores
after their fertilization.
The female gonophores consist normally of a spadix (Fig. 1B) arching over a
single, large egg (exception E. vervoorti). The spadix may be simple or branched,
which is an important taxonomic character. As the egg matures and then is fertilized
in-situ, the spadix is resorbed, the fertilized egg develops a perisarc capsule and is
attached to the pedicel below (Fig. 9E). The embryonic development to the planula
larva takes thus typically place within the capsule and while still attached to the mother
colony (comp. Mergner, 1957 and Fig. 9E). The dispersal capacity of the planula larva
is rather modest (Sommer, 1992).
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FIG. 1. Features and important terms of the Eudendriidae hydranths and gonozooids. (A)
Hydranth and its pedicel. (B) Partially atrophies hydranth (blastostyle) bearing female gono-
phores. The gonophores are very simple, a large egg and a spadix that arches over it. In later
stages after ferti lization, the spadix is lost and the encapsulated embryos attach to the pedicels
of the former blastostyle (Fig. 9D). (C) Hydranth with a whorl of male gonophores, each com-
posed of two bulbous chambers. (E-H) Important nematocyst types found in the Eudendriidae,
shown are discharged capsules. (E-F) Haplonemes, the everted tube has no thickened proximal
part. (E) Isorhiza, the everted tubular part has a constant diameter. (E) Anisorhiza, the everted
tubular part tapers constantly. (G-I) Heteroneme capsules, the everted tube is differentiated in to
a thicker basal part, the shaft, which tapers abrubtly into a thinner thread. (G) Microbasic
mastigophores, the shaft is isodiametric and shorter than 2.5 capsule lengths. (H) Microbasic
eurytele, the end of the shaft is swollen, the total length of the shaft is shorter than 2.5 capsule
lengths. (I) Macrobasic eurytele, the shaft is more than 2.5 times as long as the capsule (=macro-
basic), its end is swollen (=eurytele).

Male gonophores (Fig. 1C) typically consist of several bulbous chambers
containing the spermatogenetic cells and arranged in linear series. In the earliest stages
– in some species permanently – there is only one chamber, but as development
proceeds additional chambers are added from below. Thus the number of chambers
cannot be used as a diagnostic character although the maximal number may be
characteristic for a species.
Crucial taxonomic characters are the types and sizes of the nematocysts (Fig.
1E-I). Also the absence of desmonemes from all species is notable. The Eudendriidae
always possess small euryteles, present in large numbers on the tentacles and also in
fewer numbers in the rest of the hydranth and coenosarc epidermis. This ubiquitous
small type, also called the tentacular type, is taxonomically not important because it
does not offer much interspecific variation. However, in most species there are one or
more additional capsule types present which show considerable interspecific variation.
These complementary nematocysts are less frequent but nevertheless abundant enough
to be easily found. They never occur on the tentacles, but are confined to the hydranth
body, hypostome, the coenosarc, and sometimes the gonophores. The complementary
nematocysts are often – but not always – considerably larger than the tentacular type.
The highest concentration is found on the hydranth body, sometimes in a broad
horizontal band or in wart-like protrusions. The types of nematocysts relevant for the
Eudendriidae are shown and explained in Fig. 1E-F. In order to observe discharged
capsules, it is necessary to examine living material with a good compound microscope.
One or two hydranths are placed in small drop of seawater on a micro slide and then
gently squeezed by covering them with a cover-glass. Occasionally, there are also some
discharged capsules present in preserved material, which can be cleared by immersing
in 50% lactic acid. Examination and measurement of nematocysts requires an oil-
immersion objective that gives a final magnification of about 1000 times.
TAXONOMIC PART
FAMILY EUDENDRIIDAE L. AGASSIZ, 1862
SYNONYMS: Eudendroidae L. Agassiz, 1862: 342 [emended to Eudendriidae by Hincks,
1868]. – Myrionemidae Pictet, 1893.
DIAGNOSIS: Hydroid colony sometimes stolonal, but mostly with erect branched
stem, arising from a creeping hydrorhiza; stem, branches and hydranth pedicels
covered by perisarc, sometimes enveloping also lower half of hydranth in a cup-like
process; hydranth large, urn-shaped with undercut hypostome, one or more whorls of
solid filiform tentacles immediately below it, hydranth body sometimes with basal
tentacle-like protrusion (nematophore); near base of hydranth an epidermal groove
from which periderm is secreted, sometimes with a ring of nematocysts immediately
above groove. Reproduction by fixed sporosacs borne on the hydranth body below the
tentacles; reproductive hydranth can be partially reduced to a blastostyle or entirely
reduced. Male gonophores usually with several bulbous chambers, successive
chambers in linear series. Female gonophores sporosacs, initially with curved spadix
supporting one large egg.
REMARKS: For a taxonomic history see Calder (1988) and Marques et al.
(2000a). The family comprises only two genera, namely Eudendrium Ehrenberg, 1834
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FIG.2
Maximum Likelihood analysis of the partial 16S sequence differences of Eudendriidae samples
discussed in this publication (HKY substitution model, indels ignored). Small numbers next to
nodes indicate percent bootstrap support (only shown if >70%). The length of the sum of the
horizontal lines is a measure of the sequence difference. The taxon labels are composed of the
species name, the sampling region, followed by the EMBL/GenBank accession number or the
voucher number if the sample has the same sequence as other known sequences (if available, see
list of exmined material for each species).

and Myrionema Pictet 1893. The latter genus is characterized by a large (>35) number
of tentacles arranged in more than one whorl. In the ERMS region (European Register
of Marine Species; Costello et al., 2001), only the genus Eudendrium is present. Some
earlier Mediterranean records of Myrionema species are likely due to confusions with
E. moulouyensis (comp. Marques et al., 2000b). Another problematic species is Myrio -
nema multicornis discussed at the end of this treatise.
Genus Eudendrium Ehrenberg, 1834
TYPE SPECIES: Tubularia ramosa Linnaeus, 1758 [designation by Allman, 1872].
SYNONYMS (after Calder, 1988): Calamella Oken, 1815: 55 [invalid name, ICZN
Opinion 417]. – Corymbogonium Allman, 1861: 171. – Edendrium Allman, 1872 [incorrect
spelling]. – Erudendrium Thompson, 1899 [incorrect spelling].
DIAGNOSIS: Eudendriidae with tentacles in one whorl, of varied number but
usually fewer than 35.
REMARKS: For the taxonomic history see Calder (1988). Although Ehrenberg
(1834) translates the genus name as "Pracht-Polyp" [splendour polyp], the name is li-
kely derived from the Greek words "eu" (pleasing, good) and "dendron" (tree). The
grammatical gender is neuter.
The species are here grouped and discussed according to their complimentary
nematocyst types (instance 1 in the following key) and apparent similarity in order to
allow an easier comparison. However, this does not imply a phylogenetic order.
KEY TO EUDENDRIUM SPECIES IN THE ERMS ZONE (PROBLEMATIC SPECIES EXCLUDED):
1a complementary nematocysts are large macrobasic euryteles (shaft length
s>2.5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1b complementary nematocysts are small or large haplonemes (iso- or an -
izorhizas) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1c complementary nematocysts are microbasic euryteles (shaft length
s<2.5), either distinctly larger than tentacular euryteles or only slightly
larger (1.3 times) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1d without complementary nematocysts or these haplonemes of same size
as tentacular euryteles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2a macrobasic euryteles in buttons on hydranth body . . . . . . . . . . . . . . . . . . . . . 3
2b macrobasic euryteles scattered on hydranth body, not in buttons . . . . . . . . . . 4
3a colonies large, usually polysiphonic, shaft of intact macrobasic eurytele
in 2.5 loose coils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. glomeratum
3b colonies monosiphonic, female blastostyles after fertilization reduced to
nematocyst knobs, shaft of intact macrobasic eurytele in more than 2.5
coils along capsule wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. cnidoferum
4a macrobasic euryteles with 3-5 coils oblique to long axis, gonochoristic
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. album
4b macrobasic euryteles with coils along long axis, female sporosac often
with sperm chamber, usually on the Mediterranean sea grass Posidonia
oceanica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. simplex
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4683

5a haplonemes small (< 10 μm), colonies monosiphonic or stem base
composed of a few tubes only . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5b strongly polysiphonic, no cnidophores, haplonemes large (> 20 μm)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. carneum
6a spadix of female sporosac bifid, some hydranths with cnidophores, large
colonies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. racemosum
6b spadix of female sporosac simple, complimentary nematocysts are small
haplonemes of same size as tentacular euryteles, presence variable, often
absent, colonies small and delicate . . . . . . . . . . . . . . . . . . . . . . . . E. capillare
7a shaft in intact complimentary microbasic euryteles straight . . . . . . . . . . . . . . 8
7b shaft in intact complimentary microbasic euryteles with a coil . . . . . . . . . . . 15
8a colonies large, trunk or base polysiphonic . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8b colonies monosiphonic or stem-base made up of a few tubes only . . . . . . . . 11
9a complementary euryteles scattered on body, colony tree-like . . . . . . E. rameum
9b complementary euryteles forming a contiguous belt on body . . . . . . . . . . . . 10
10a colony more tree-like, stems usually with bark-like covering, hydranths
large (>0.4 mm diameter), blastostyles aggregated on upper side of
branches, pedicels relatively short . . . . . . . . . . . . . . . . . . . . . . . . E. annulatum
10b colonies more bush-like, stem without bark-like covering, hydranths
small (<0.3 mm diameter), blastostyles dispersed . . . . . . . . . . . . E. arbuscula
11a with zooxanthellae in gastrodermis . . . . . . . . . . . . . . . . . . . . . E. moulouyensis
11b without zooxanthellae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
12a complimentary eurytele large, more than two times as large as tenta cular
euryteles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
12b complimentary eurytele small, only 1.3 times as large as tentacular
capsules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. capillaroides n. sp.
13a gonophores develop on normal or slightly reduced hydranths . . . . . . . . . . . 14
13b gonophores develop on blastostyles without vestiges of a hydranth, shaft
of discharged large euryteles with thick spines . . . . . . . . . . . . . E. cf. merulum
14a colonies much branched, monosiphonic or exceptionally with few tubes
near base, large euryteles scattered on body, spadix without swelling
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. ramosum
14b colonies sparingly branched, large euryteles concentrated in belt on
body, spadix of female sporosac with distal triangular swelling (axe- like
shape) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. calceolatum
15a colonies usually polysiphonic, perisarc annulated throughout, thick,
brown, lower half of hydranth in perisarc collar, coil size of shaft in large
eurytele rather small . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. vaginatum
15b colonies monosiphonic, perisarc thin, with smooth and annulated
stretches, hydranth without perisarc collar, coil size of shaft in large
eury tele about 1/4 or more of capsule length . . . . . . . . . . . . . . . . . E. unispirum
16a female gonophores with spadix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
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16b female gonophores without spadix, eggs attached via long pedicels to
normal hydranths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. vervoorti
17a colonies polysiphonic, some hydranths modified into long nemato -
phores, without complimentary nematocysts . . . . . . . . . . . . . . . . . . E. armatum
17b colonies monophonic, no nematophores, without complimentary nema-
tocysts or sometimes with small haplonemes of the same size as tenta-
cular capsules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. capillare
Eudendrium glomeratum Picard, 1952 Figs 3-4
Eudendrium ramosum. – Browne, 1897: 243. – Motz-Kossowska, 1905: 54, pl. 3 fig. 16. [not
Eudendrium ramosum (Linnaeus, 1758)]
Eudendrium arbuscula. – Schneider, 1898: 477. [not Eudendrium arbuscula Wright, 1859]
Eudendrium pusillum. – Jäderholm, 1916: 3. – Watson, 1985: 213. [not Eudendrium pusillum
Lendenfeld, 1885: 352, = E. lendenfeldi Briggs, 1922]
? Eudendrium indopacificum Stechow, 1924: 59. [new name for E. pusillum in Thornely, 1904]
Eudendrium glomeratum Picard, 1951b: 260. [nomem nudum]
Eudendrium glomeratum Picard, 1952: 338, new name. – Castric & Michel, 1982: 82, fig. –
Watson, 1985: 213, figs 89-94. – Boero et al., 1986: 81-85, fig. 1. – Boero & Cornelius,
1987: 244. – Marinopoulos, 1992: 59, fig. 1.9. – Watson, 1999: 7, fig. 5A-D. – Marques
et al., 2000a: 96, figs 53-56. – Marques et al., 2000b: 205. – Peña Cantero & García
Carrascosa, 2002: 29, fig. 4c-f. – Puce et al., 2005: 202, figs 1d, 2i.
MATERIAL EXAMINED: MHNG INVE29456; Mediterranean, France, Banyuls-sur-Mer,
depth 2m, 14 Sept. 1995; fertile female. – MHNG INVE29457; Mediterranean, France, Banyuls-
sur-Mer, 8 March 1993; 10 cm high, polysiphonic, infertile. – MHNG INVE32159;
Mediterranean, Spain, Mallorca, Cala Murada; depth 2m; 27 July 2001; small polysiphonic co-
lony on red algae, fertile female, hydranths intensively orange; 16S sequence accession number
AM991302. – MHNG INVE39462; Mediterranean, France; 26 Nov. 1953, depth 40m. – MHNG
INVE39473; Mediterranean, France, Marseille, Riou-Impériaux de Terre; depth 20m; 20 March
1966, two large infertile colonies. – MHNG INVE39717; Mediterranean, France, Marseille;
depth 40m; 28 Sept. 2004; 15 cm colony, hydranths reddish; 16S sequence accession number
AM991301. – Italy, Sardinia, depth 25m; October 2005; fertile female, 5 cm colony; in private
collection of Dr S. Puce.
DIAGNOSIS: Colonies usually tall, polysiphonic when fully grown, with large
macrobasic euryteles arranged in buttons or belt around hydranth body. Male and
female blastostyles atrophied; spadix unbranched when immature, shed when mature.
Hydranths red.
DESCRIPTION: Colonies large, bushy or tree-like, irregularly branching, when
reproductive usually stems and some branches polysiphonic, monosiphonic stems can
occur. Perisarc thick, smooth, occasionally some annulated stretches, usually at bases
of branches. Hydranths with 15-27 tentacles (mostly 20-22), on hydranth body a ring
composed of several nematocyst buttons (4-10), these buttons can coalesce into an
irregular band, buttons can also be scattered on hydranth body. Tentacles with nema -
tocysts along entire length but density decreasing towards proximal, in bands with
arrays of 3-4 capsules, capsules oriented parallel to surface and tentacle surface thus
smooth. Colours: older perisarc brown; hydranth characteristically red.
Male gonophores two-chambered and borne on blastostyles lacking tentacles at
all stages; with or without terminal buttons; clusters of macrobasic euryteles can be
present at base of blastostyle and at end of gonophores, not always in the terminal
buttons.
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FIG. 3. Eudendrium glomeratum Picard, 1952, after preserved Mediterranean material, except E
(native capsules). (A) Silhouettes of typical colonies (MHNG INVE39473), scale bar 2 cm. (B)
Hydranth with characteristic nematocyst buttons (arrow), scale bar 0.5 mm. (C) Young female
blastostyle (MHNG INVE32159), scale bar 0.2 mm. (D) Male blastostyle, note nematocysts at
base of blastostyle, material from Sardinia, scale bar 0.2 mm. (E) Nematocysts (MHNG
INVE39717): intact and discharged microbasic eurytele, two intact macrobasic euryteles in side
and frontal view, above discharged macrobasic eurytele, scale bar 10 μm.

Female gonophores develop on reduced hydranth with few tentacles (up to 8),
hydranth body small, hypostome absent, 4-6 gonophores per blastostyle, spadix
simple, with one or more nematocyst buttons near tip, spadix later atrophied, also
tentacles are lost during later development, eggs ultimately attached to blastostyle
pedicels. Incipient oogonia visible in coenosarc of branches.
Nematocysts: microbasic euryteles, on tentacles; macrobasic euryteles in
nematocyst buttons, shaft in intact capsule in about 2-3 loops following long axis of
capsule, discharged about four times the length of the capsule, barbed.
DIMENSIONS: Height of reproductive colonies from a few cm to about 15 cm;
hydranth diameter about 0.5 mm, variable even within the same colony; diameter of
basal stem tubes 0.4-0.5 mm. Macrobasic euryteles in Mediterranean animals
(22-33)x(9.5-13.5)μm, r= 2.2-2.4 (Marinopoulos, 1992; Marques et al., 2000b; Peña
Cantero & García Carrascosa, 2002; own data). Australian values show more variation
(Watson, 1985; 1999). Microbasic euryteles (6-10)x(3-5)μm, r= 2.1-2.3 (Peña Cantero
& García Carrascosa, 2002; Watson, 1985; own data).
BIOLOGY: Occurs on various solid substrata in depths of 0-200 m (Peña Cantero
& García Carrascosa, 2002), more commonly in depths of 10-40 m (Fey, 1970; Boero
et al., 1986). In the Mediterranean, fertile colonies can be found all year round (Peña
Cantero & García Carrascosa, 2002; own data), but the peak of reproduction seems to
687
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 4
Eudendrium glomeratum Picard, 1952, native macrobasic euryteles; MHNG INVE39717.

be during autumn and winter (Boero, 1984; Boero et al., 1986). In the Atlantic, repro-
ductive colonies have been found from June to October (Fey, 1970; Peña Cantero &
García Carrascosa, 2002). More ecological data are given in Boero (1981), Boero &
Fresi (1986), Boero et al. (1986), Arillo et al. (1988), and Bavestrello et al. (1994).
Some colonies can be aggregates of colonies (Bavestrello & Cerrano, 1992).
DISTRIBUTION: Rather common and widespread in the western and eastern
Mediterranean, including the African and Israeli coasts (see e. g. Marques et al., 2000b
and 2000b; Peña Cantero & García Carrascosa, 2002). In the western Atlantic known
from the British Isles (Boero & Cornelius, 1987) (not in North Sea), Brittany (Teissier,
1965; Fey, 1970; Castric et al., 1987), Northern Spain (Medel & López-González,
1996). Further records are known from Australia (Watson, 1985; 1999) and Brazil
(Marques, 1993; cited in Peña Cantero & García Carrascosa, 2002). Type locality:
Mediterranean, France, Banyuls-sur-Mer (Boero & Cornelius, 1987).
REMARKS: With its large colonies and the macrobasic euryteles in warts on the
hydranth, Eudendrium glomeratum is relatively easily identifiable. Despite this and its
relative abundance in the Mediterranean, it was described and recognized rather late.
Many older records of E. rameum and even E. ramosum were therefore actually based
on E. glomeratum (Marques et al., 2000a).
Eudendrium cnidoferum Stechow, 1919 Fig. 5
Eudendrium armatum Jäderholm, 1907: 372. – Jäderholm, 1909: 52, pl. 4 figs 7-9.
[not Eudendrium armatum Tichomiroff, 1887]
Eudendrium cnidoferum Stechow, 1919: 154, new name.
TYPE MATERIAL EXAMINED: SNHM type 4274, Syntype colonies of Eudendrium arma-
tum Jäderholm, 1907; loc. Bohuslän.
DIAGNOSIS: Monosiphonic colonies, hydranths with nematocyst buttons
containing large macrobasic euryteles, female blastostyles after fertilization reduced to
nematocyst knobs.
DESCRIPTION: Colonies on algae, monosiphonic, much branched, branching ir-
regular, branches long. Perisarc mostly smooth, some annulation present, annulation
usually present at origin of new branches and hydranth pedicels. Hydranths typical for
genus but relatively small, 22-24 tentacles, near base wart-like nematocyst clusters
with macrobasic euryteles.
Only advanced, presumably fertilized, egg stages present, these encapsulated
and attached in whorls around pedicels of former blastostyles (Fig. 5B-C). Former
blastostyle reduced to nematocyst knobs at end of pedicels.
Nematocysts: tentacular microbasic euryteles and large macrobasic euryteles in
nematocyst buttons, shaft discharged more than four times as long as capsule, in un-
discharged capsule shaft coiled several times, coils along capsule wall and apparently
filling capsule.
DIMENSIONS: Stems about 6 cm high, basal stem diameter 0.25 mm, hydranth
pedicel diameters 0.14-0.17 mm. Preserved microbasic euryteles from tentacles
(7-7.5)x(3-3.5)μm, r= 2-2.5; macrobasic euryteles (20.5-24)x(7.5-8.5)μm, r=2.6-3.0.
DISTRIBUTION: Only known from the type locality, Bohuslän, Sweden.
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REMARKS: When Jäderholm (1907) described Eudendrium armatum as new
species, he was likely unaware that this name was already in use as Eudendrium
armatum Tichomiroff, 1887. Stechow (1919) therefore proposed the replacement name
E. cnidoferum, thus becoming also the author of the taxon. The species is only known
from its type specimen and it was characterized by Jäderholm (1909) by what he consi-
dered the blastostyles. The eggs are attached in a whorl around a perisarc covered
pedicel, the latter ending in several buttons full of large nematocysts (Fig. 5B, D),
resembling the ends of tentaculozooids of Hydractinia echinata. Jäderholm considered
them to be specialized nematophores. A re-examination of the type specimen
confirmed Jäderholm’s observation, but the blastostyles must be re-interpreted.
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EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 5
Eudendrium cnidoferum Stechow, 1919, after syntype material, A-C modified from Jäderholm
(1909). (A) Several stems, scale bar 1 cm. (B-C) Branches with encapsulated eggs/embryos. (D)
Terminal portion of a blastostyle pedicel with nematocyst buttons. (E) Small microbasic eurytele
and large macrobasic eurytele, the internal structure was only indistinctly visible, bar 10 μm.

Additionally, although only very few hydranths are left, these have nematocyst buttons
near the base of hydranth, just like in E. glomeratum (Fig. 3B). The gonophores are
actually encapsulated – likely fertilized – eggs or embryos attached to the former
pedicel of the blastostyle, as usually found in the final stages of the sequence of the
development of the female sporosac (see General Morphology section). As in other
Eudendrium species, the blastostyles became reduced once the eggs had been fertilized
and what we see are likely only the vestiges of the former blastostyles. As also the blas-
tostyles can have nematocyst buttons (e. g. E. glomeratum, Fig. 3C-D), these buttons
might be the sole remainder of the former blastostyle. Nevertheless, they could be a
constant feature of the species and perhaps allow a distinction from the otherwise
almost identical E. glomeratum. There are only a few traits that would allow dis tinction
of E. glomeratum from E. cnidoferum. The latter forms a monosiphonic colony, while
the former species forms normally polysiphonic colonies, although Marques et al.
(2000b) also report monosiphonic colonies. Perhaps also the undischarged large eury-
teles of the two species differ slightly. While in E. glomeratum the shaft makes only a
few loose coils (Fig. 4), it seems to fill the capsule in E. cnidoferum (Fig. 5E).
However, this observation is to be taken with some caution as the old material of E.
cnidoferum did not permit a detailed, reliable observation of this trait.
Eudendrium cnidoferum remains an insufficiently known species and a conclu-
sive evaluation of the status of can only be made once new material from Bohuslän
becomes available. It seems nevertheless advisable to retain it as a valid species for the
time being.
Eudendrium album Nutting, 1896 Figs 6-7
Eudendrium album Nutting, 1896: 146. – Nutting, 1898: 362, pl. 14, fig. 1. – Nutting, 1901: 334,
fig. 11. – Kingsley, 1910: 20, pl. 2 fig. 11. – Fraser, 1912: 348, fig. 5 A-B. – Billard, 1927:
327. – Fraser, 1944: 61, pl. 7 fig. 32. – Leloup, 1947: 107: 18, fig. 9. – Leloup, 1952:
124, fig. 61. – Calder, 1971: 45, pl. 3 fig. B. – Watson, 1985: 185. – Marques et al.,
2000a: 77, figs 1-7. – Faasse & Vervoort, 2005: 58, figs 1-2.
not Eudendrium album. – Pennycuik, 1959: 167.
Eudendrium fragile Motz-Kossowska, 1905: 58, fig. 1, pl. 3 fig. 17. new synonym
Eudendrium fragile. – Marinopoulos 1992: 59, fig. 1. 11. – Boero & Freesi, 1986: 141. –
Marques et al., 2000a: 206. – Puce et al. 2005: 202, figs 1c, 2d, 2h.
Eudendrium islandicum Schuchert, 2000: 417, fig. 4. new synonym
Eudendrium islandicum Schuchert, 2001a: 29, fig. 17.
MATERIAL EXAMINED: BMNH 1912.12.21.85; as Eudendrium album; marked with red
ink as “? type specimen”; A. M. Norman Collection; England, Plymouth; infertile, nematocysts
not identifiable. – BMNH 1948.9.8.83; as Eudendrium album; England, Plymouth; 11 May
1898; female; E.T. Browne collection; has typical macrobasic euryteles. – BMNH 1948.9.8.81;
as Eudendrium album; England, Plymouth; 11 May 1898; Nemertesia antennina; infertile; coll.
E.T. Browne; nematocysts not preserved. – MHNG INVE37297; as Eudendrium album; France,
Normandy, Cotentin, Herquemoulin, Treize Vents; 22 Aug. 2005; on Halopitys incurvus; male
and female colonies; male sporosacs on fully formed hydranth, female likewise, 16 S sequence
AM991298. – Norway, near Bergen, Flesland beacon, depth 20-100m; 20 June 2006; infertile
colony on rock; has typical macrobasic euryteles; not preserved, AM991299. – BELUM Md617;
Northern Ireland, Strangford Lough Narrows, W of Rue Point; 54.365°N 05.542°W; depth 7m;
02 Aug. 1983; female. – BELUM Md623; Northern Ireland, Strangford Lough Narrows, W of
Rue Point; 54.365°N 05.542°W; depth 25m; 03 Aug. 1983; infertile. – BELUM Md618;
Northern Ireland, Strangford Lough Narrows, W of Rue Point; 54.365°N 05.542°W; 25m; 03
Aug. 1983; female. – BELUM Md107; Northern Ireland, Mulroy Bay, Cranford, Broad Water,
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Deegagh Point; 55152°N 07.690°W; depth 10m; 25 March 1978; infertile. – BELUM Md106,
as Eudendrium ramosum; Northern Ireland, Strangford Lough, E of Strangford; 54.373°N
05.554°W; depth 3m; 07 June 1976; female.
DIAGNOSIS: Colonies monosiphonic, small, gonochoristic; male and female
sporosacs on normal hydranths; spadix simple; complementary nematocyst macro basic
eurytele; shaft inside capsule coiled obliquely in relation to long capsule axis, coil
diameter max. 2/3 of capsule.
691
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 6
Eudendrium album Nutting, 1896; after preserved material from the English Channel. (A)
Colony from intertidal region, scale bar 0.5 mm. (B) Hydranth with female sporosacs, scale bar
0.2 mm. (C) Hydranth with male sporosacs, same scale as B. (D) Nematocysts: microbasic
eurytele; two macrobasic euryteles, left frontal view, right lateral view. Scale bar 10 μm.

DESCRIPTION: Colonies arising from creeping, branching stolons; stems mono-
siphonic, irregularly branched, 1-20 hydranths per shoot (up to 50 possible), shallow-
water colonies small, Mediterranean colonies sometimes stolonal, cold-water colonies
larger. Perisarc smooth with some corrugated or annulated stretches, perisarc of stem
brown to yellowish, branches yellowish-brown fading to colourless. Hydranths cup-
shaped as somewhat tapering towards base, hypostome rounded, large, around 17-22
tentacles; basal third of tentacles nearly free of nematocysts, in more distal region
nematocysts in rings, capsule almost perpendicular to tentacles thus rendering it spiny.
Colonies gonochoristic. Living hydranths of English Channel white to cream coloured,
perisarc of preserved material yellowish.
Female gonophores develop in one whorl on body of a normally developed
hydranth, about six sporosacs, initially with a simple curved spadix; hydranths can be
somewhat reduced with ongoing gonophore maturation.
In older stages spadices shed and the embryos in their transparent capsules
attached irregularly along the pedicel of the former blastostyle.
Male gonophores 2-3 (mostly 2) chambered, arising as single whorl from lower
part of the body of either normally developed or only very slightly reduced hydranths,
6-8 gonophores, with or without distal button on last chamber, button if present without
concentration of nematocysts. Nematocysts: small microbasic eurytele on tentacles,
almond-shaped; larger macrobasic eurytele, shaft in intact capsule in 4-5 coils that are
oblique in relation long axis of capsule (in side view), confined to upper 2/3 of capsule
(Figs 6D, 7).
DIMENSIONS: Colony height is from a few mm in the intertidal region to 7 cm in
deep waters. Hydranths 0.4-0.7 mm. Diameter of stems at base 0.12-0.20 mm,
branches thinner. Nematocysts (preserved material): microbasic eurytele (7-8)x(2.5-
4)μm, r = 2.0-2.8; macrobasic eurytele, size (18.5-27)x(7.5-14)μm, r = 2.0-2.7, s > 5.
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FIG. 7
Eudendrium album Nutting, 1896; nematocysts, living material from Norway. The two images
at right depict the same capsules, but in different focusing planes.

BIOLOGY: Occurs from the intertidal to about 1000 m depth (deep-water records
as E. islandicum). In the English Channel, gonophores are present from at least January
to August (Russell, 1957, own observations). It occurs on stones, algae and other
hydroids. More data on the biology of the American population are given in Calder
(1971, 1976, 1990).
DISTRIBUTION: Mediterranean to North Atlantic. Only a minority of the known
records are based on identifications that include nematocyst information. Without this
information, identifications should be considered as tentative only. In the eastern
Atlantic ranging from Galicia (Spain) to Norway (e. g. Nutting, 1898; Billard, 1927;
Leloup, 1947, 1952; Russell, 1957; Teissier, 1965; Altuna Prados, 1994; Medel &
López-González, 1996; Marques et al., 2000b; Faasse & Vervoort 2005; this study).
Has also been recorded in the Black Sea (Manea, 1977). In the western Mediterranean,
it is known under the name E. fragile (Motz-Kossowska, 1905; Boero & Freesi, 1986;
Marinopoulos, 1992; Marques et al. 2000b; Puce et al., 2005). As E. islandicum it has
been recorded from Iceland (Schuchert, 2000) and southern- to southwestern
Greenland (Schuchert, 2001). Along the American continent it is known from the Gulf
of St. Lawrence to Florida (Fraser, 1944; Calder, 1971, 2003). The following records
must be confirmed again: California (Fraser, 1948) and Gulf of Mexico (Deevey,
1954). Type locality: Shallow waters near Millbay Channel, Plymouth, Great Britain.
REMARKS: Nutting (1898) regarded the small colony size and the white
hydranths as diagnostic for this species. Colour is often not a reliable trait to distin-
guish species and the identity of E. album from Plymouth is not entirely clear as no
unambiguous type material exists. The BMNH has a specimen from Plymouth marked
with red ink as "? type". The specimen is from the Norman collection and there is no
indication that it was obtained from Nutting. Furthermore, the material is infertile and
does thus not correspond to Nutting's first description where he mentions fertile
material. It is thus unlikely that it is the type specimen. The nematocysts of this
specimen are too poorly preserved to be identified. Other potential type material could
not be found and it must be assumed that no type material has survived (a potential type
specimen formerly present in the Smithsonian Institution is likely lost; Dr A. Collins,
pers. comm.). The BMNH has other, non-type samples of E. album from Plymouth,
two of which still have identifiable nematocysts. The colony morphology of both
match Nutting's description. Based on the nematocysts, one of them has macrobasic
euryteles, while the other has apparently different nematocysts (see Eudendrium
unispirum).
A search for Eudendrium species at and near the type locality (Millbay Channel,
Plymouth) in June 2007 produced only E. capillare.
The scope and identity of Eudendrium album is thus not entirely clear, but
Watson (1985) and Marques et al. (2000a) have re-defined this species by stating that
its identification depends on the presence of macrobasic euryteles. As this form is
apparently not uncommon in the English-Channel (see material examined) and thus
might correspond to the Nutting’s original species, it is advisable to maintain this
usage. In order to stabilize the nomenclature, it might be necessary to designate a
neotype based on fertile material of which the 16S and COI sequences are known.
693
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4

Eudendrium fragile Motz-Kossowska, 1905 as re-defined in Marinopoulous
(1992), Boero & Fresi (1986), and Marques et al. (2000b), appears indistinguishable
from E. album and both are here regarded as conspecific.
Eudendrium islandicum Schuchert, 2000 is not objectively separable from E.
album. Eudendrium islandicum has somewhat larger colonies than E. album, a feature
likely attributable to the deeper and colder waters it was taken from. Apart from the
colony size and the biogeographic zone (cold boreal to Arctic waters), there is thus
nothing that would allow distinguishing them and they must therefore be regarded as
conspecific.
The 16S sequences of two colonies of E. album, one originating from the inter-
tidal of English Channel, the other from deeper waters in Norway, could be compared
(Fig. 2). Although both colonies and their nematocysts appeared indistinguishable, the
sequences were rather divergent, suggesting a possible cryptic speciation (or E. islan-
dicum could nevertheless be valid, separable on biogeographic grounds).
Eudendrium simplex Pieper, 1884 Fig. 8
Eudendrium simplex Pieper, 1884: 150. – Motz-Kossowska, 1905: 56, pl. 3 figs 18-19. –
Stechow, 1919: 30. – Marques et al., 2000b: 205. – Bouillon et al., 2004: 61, figs
36M-P.
Eudendrium motzkossowskae Picard, 1952: 339. – Marques et al., 2000b: 206, synonym. –
Boero, 1981: 188, fig. 4. – Marinopoulos, 1992: 59, fig. 1.10. – Boero & Freesi, 1986:
141.
? Eudendrium motzkossowskae. – Millard & Bouillon, 1974: 17, fig. 3J-K. – Millard, 1975: 84,
fig. 29G-H.
MATERIAL EXAMINED: MHNG INVE27128, as Eudendrium motzkossowskae; Mediter -
ranean, Mallorca, Cala Murada, depth 4m, on Posidonia oceanica; 26 Aug. 1999; male and
female colonies. – Ionian Sea, Italy, S. Caterina; 27 Nov. 2001 and 11 Oct. 2006; fertile colonies;
preserved material in pers. collection Doris De Vito.
DIAGNOSIS: Usually on Posidonia oceanica, stolonal or sparingly branched
colonies, large macrobasic eurytele with several coils along long axis, blastostyles
normal hydranths, spadix of female sporosacs often with a chamber containing male
gametes.
DESCRIPTION: Colonies stolonal or sparingly branched with up to four hydranths
per stem. Stolons creeping, ramified. Perisarc of stems smooth with some annulated or
corrugated stretches, variable. Hydranths typical for genus, around 20 tentacles, basal
grove visible, above basal grove large nematocysts, but not dense, few more large
capsules scattered on other parts of hydranth. Male and female colonies separate,
gonophores develop on normal hydranths that are not or only minimally reduced.
Male blastostyles with 1-4 sporosacs, two-chambered, no terminal nematocyst
button (Fig. 8D).
Female blastostyles with 2-5 sporosacs, spadix simple, curved, bearing few
scattered nematocysts, spadix in advanced stage often with one or rarely more bump-
like swelling due to a chamber containing spermatogenic cells (Fig. 8C). Fertilized
eggs form membranous perisarc capsule and get attached to pedicels of blastostyles
(Fig. 8B).
Nematocysts: small microbasic euryteles on tentacles; large macrobasic eury -
teles, discharged shaft very long (r>4), densely barbed (holotrichous), shaft in
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695
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 8
Eudendrium simplex Pieper, 1884; after preserved Mediterranean material. (A) Stem with two
hydranths, scale bar 0.5 mm. (B) Blastosyle (gonozooid) with developing female sporosacs and
two encapsulated embryos attached to pedicel, scale bar 0.1 mm. (C) Optical section of female
sporosac with mass of spermatogenic cells on spadix, scale bar 50 μm. (D) Blastostyle with male
sporosacs, same scale as B. (E) Undischarged nematocysts: microbasic and macrobasic eury -
teles, scale bar 10 μm.

undischarged capsule in more than four coils along the capsule wall and oriented
parallel to long axis.
DIMENSIONS: Stems up to 12 mm, hydranth pedicel diameter 0.08-0.090 mm,
stem diameter at base ca. 0.1 mm, hydranth height 0.25-0.3 mm, encapsulated embryos
0.2-0.25 mm. Microbasic euryteles (6-6.5)x(2.5-3.5)μm, r=2.0-2.6. Macrobasic
euryteles (16-19)x(6.5-8.5)μm, r=1.7-2.5. For more nematocyst measurements see
Marinopoulos (1992) and Marques et al. (2000b).
BIOLOGY: Occurs in shallow water (down to 15 m), predominantly or perhaps
exclusively on Posidonia oceanica. Mature from April to November (Gili & Garcia
Rubies, 1985; Bouillon et al., 2004; own data).
DISTRIBUTION: Mediterranean (Marques et al., 2000b). The records from
southern Africa (Millard & Bouillon, 1974; Millard, 1975; as E. motzkossowskae) are
uncertain as no hermaphroditic sporosacs were observed. Type locality: Dalmatian
coast, Adriatic Sea.
REMARKS: The synonymy of this species was outlined by Marques et al.
(2000b). If present, the unique hermaphroditic sporosacs allow a reliable identification
of this species. Its occurrence on Posidonia oceanica also helps to identify it.
Eudendrium fragile, a subjective synonym of E. album, is otherwise quite similar, but
the macrobasic euryteles differ slightly (comp. Figs 7 and 8E).
Eudendrium racemosum (Cavolini, 1785) Figs 9-10
Sertolara racemosa Cavolini, 1785: 160, pl. 6 figs 1-7, 14-15.
Sertularia racemosa Gmelin, 1788: 3854.
Eudendrium racemosum. – Ehrenberg, 1834: 296. – Allman, 1872: 341. – Morri, 1981: 59, fig.
18, pl. 1 fig. – Gili, 1982: 42, fig. 10. – Gili & Castello, 1985: 11, fig. 2. – Watson, 1985:
204, figs 63-67. – Marinopoulos, 1992: 60, figs 1.1, 2, 5. – Marques et al., 2000a: 100,
figs 67-70. – Marques et al., 2000b: 207. – Peña Cantero & García Carrascosa, 2002: 33,
fig. 6. – Puce at al., 2005: 302, figs. 1f, 2m. – Puce at al., 2006: 622, fig. 4a-c.
? Eudendrium racemosum. – Stechow, 1913: 63. – Yamada, 1954: 5, fig. 4. – Hirohito, 1988: 84,
fig. 29.
not Eudendrium racemosum mucronatum Billard, 1926: 88, fig. 8.
MATERIAL EXAMINED: BELUM Md1005; Atlantic, France, Brittany, Anse de Camaret; 4
Aug. 1986. – MHNG INVE25854; France, Corsica, Calvi; depth 2m; 6 Jul. 1992; fertile female
and male colonies. – MHNG INVE26505; Mediterranean, France, Banyuls-sur-Mer; depth 4m;
male colony; 12 Jul. 1999. – MHNG INVE27671; Spain, Canary Islands, Lanzarote; 23 Sep
1999; depth 25-30m; male. – MHNG INVE27672; Canary Islands, Tenerife, Radazul; 4 Oct.
1999; depth 20-30m; fertile. – MHNG INVE29810; Mediterranean, Spain, Mallorca, Cala
Murada; 14 Aug. 2000; depth 2m; 16S sequence AY787896. – MHNG INVE32164;
Mediterranean, Spain, Mallorca, Cala Murada; 30 Jul. 2001, depth 1 m. – MHNG INVE39448;
Mediterranean, port of Monaco, artificial cave; 6 Jul. 2001; depth 9m. – MHNG INVE49719;
Mediterranean, France, Marseille, Impériaux de Terre; 14 Jun. 2004; on rock; male; 16S
sequence AM991307. – MHNG INVE49718; Mediterranean, France, Marseille, Grand Conglu;
depth 3m; 16 Jun. 2004; on rock; female. – MHNG INVE49884; Italy, Naples; 23.12.1891; male
and female stems. – MHNG INVE49885; Italy, Naples, Nisida; coll. ca. 1900, male. – MHNG
INVE25958; Italy, Naples, coll. 1892. – Mediterranean, France, Banyuls-sur-Mer; 4m; male
colony; 7 Nov. 1997; material not deposited; 16S sequence AM991297. – Mediterranean, Spain,
Mallorca, Cala Murada; under rock overhang, depth 1-2m; 13 Jul. 2006, female; not deposited;
16S sequence identical to AY787896 – Mediterranean, Spain, Mallorca, Cala Murada; under
rock overhang, depth 1-2m; 13 Jul. 2006, female; not deposited; 16S sequence identical to
AY787896.
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DIAGNOSIS: Large colonies, mostly monosiphonic, some hydranths with cnido-
phores; blastostyles reduced; spadix of female gonophore branched; complementary
nematocysts are isorhizas.
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EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 9
Eudendrium racemosum (Cavolini, 1785), after preserved Mediterranean material. (A) Colony
silhouette, scale bar 10 mm. (B) Hydranth with basal nematophore, scale bar 0.5 mm. (C) Male
blastostyle, scale bar 0.5 mm. (D) Gonozooid with female sporosacs, note bifid spadix, scale bar
0.5 mm. (E) Schema of developmental stages on female blastostyle, the numbers indicate the
number of nuclei during the embryonic development; figure modified after Mergner (1957). At
the top, the eggs are held by the spadices, they are not yet fertilized. Fertilization has taken place
in the eggs below, starting with the two nuclei stage to the 64 nuclei stage. Through the conse-
cutive growth of the blastostyle the embryos come to lie more proximally and are ultimately
attached to the pedicel. They are enveloped by a periderm membrane. (F) Nematocysts as pairs
of discharged and native capsule: microbasic euryteles and basitrichous isorhizas.

DESCRIPTION: Colonies much branched, often quite regular, bushy to tree-like.
Stems usually monosiphonic, large colonies can be somewhat polysiphonic. Perisarc
annulation of variable extent, intermittent with smooth regions. Hydranths typical for
genus, 25-34 tentacles, frequently with tentacle-like process from lower part of
hydranth body (cnidophore), length of cnidophore 1-3 times the size of hydranth,
thicker than tentacles. Nematocysts on tentacles present in rings along entire length but
density decreasing towards proximal, capsules erect and tentacle surface thus spiny. At
lower fifth of hydranth body basal groove with origin of perisarc, perisarc here filmy
and very thin (only visible at high magnifications). Above groove usually a concen -
tration of mastigophores. Colonies dioecious.
Male gonophores develop on reduced hydranths, may have initially small
tentacles, later atrophied; mature male sporosacs in a dense tuft at ending of a branch,
each gonophore with 3-4 chambers, sometime terminal button, without dense nema -
tocyst cluster.
Female gonophores develop on reduced (1/3 size) hydranths that are later
completely atrophied. Gonophores typical for genus but spadix of younger gonophores
bifid, may be lost in mature gonophores. Fertilized eggs encapsulated and attached to
perisarc of blastostyle pedicels.
Nematocysts: microbasic euryteles on tentacles and atrichous or basitrichous
isorhizas concentrated above basal groove.
Polyps whitish to light orange-pink, eggs in gonophores dark orange-red,
perisarc brown.
DIMENSIONS: Stems 2-12 cm high, colonies from deeper waters up to 25 cm
(Motz-Kossowska, 1905). Hydranths 0.5-1 mm, nematophore length 0.4-0.6 mm,
hydranth pedicel diameter about 0.15 mm, diameter of stem at base 0.33-0.50 mm.
Nematocysts: isorhizas (8-9)x(3.5)μm; microbasic euryteles (7-8)x(2.5-3.5)μm.
BIOLOGY: In the Mediterranean, E. racemosum occurs rather abundantly in the
first few metres, but it may be found in deeper waters up to 125 m depth (Motz-
Kossowska, 1905; Boero & Fresi, 1986; Marques et al., 2000b; Peña Cantero & García
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FIG. 10
Eudendrium racemosum (Cavolini, 1785), native nematocysts, scale bar 10 μm. (A-B)
Undischarged isorhizas. (C) Discharged isorhiza. (D) Microbasic euryteles. (E) Discharged
euryteles.

Carrascosa, 2002). It grows on rocks, concretions, barnacles, mussels, gorgonians, and
algae. It is present throughout the year but is rare from December to February when it
likely overwinters as a stolonal system. Fertile animals can be found from March to
December, the main reproductive season seems to be during the summer.
More ecological data are given in Palombi (1940), Gili & Ros (1985), Barange
et al. (1987), Sommer (1992), Azzini et al. (2003). Aspects of its feeding behaviour and
ecology are described in Barange (1988), Barange, & Gili (1988), and Puce et al.
(2002).
OTHER DATA: Details of the histology, gametogenesis, and development are
given in Weismann (1883), Ishikawa (1887), Neppi (1917), Mergner (1957), Hanisch
(1970), Sommer (1990). The egg maturation is also shown in Fig. 9E. Regeneration
was studied by Billard (1904). Predation and the use of its nematocysts by nudibranch
gastropods are described by Martin (2003), Martin & Walther (2002, 2003).
DISTRIBUTION: In the Mediterranean, this is a very common and easily
obtainable hydroid. It occurs in the entire Mediterranean, this along the European,
Asian and African shores (see references in Marques et al., 2000b; Peña Cantero &
García Carrascosa, 2002). It also occurs in Mediterranean lagoons (Morri, 1981). In the
Atlantic, it is quite rare. Its northernmost records are from Brittany (Castric-Fey et al.,
2001; this study). It is present along the Iberian Peninsula (Medel & Lopez Gonzalez,
1996), the Canaries (this study), and western Africa (Leloup, 1940; Picard, 1951a;
Buchanan, 1957; Bouillon et al., 1995). In the Indian- and Pacific Ocean it has been
found in the Seychelles, (Millard & Bouillon, 1973), tropical Australia (Watson, 1985),
Vietnam (Leloup, 1937), Indonesia (Puce et al., 2006), and Japan (Yamada 1954,
Hirohito, 1988). The Japanese samples had strongly polysiphonic colonies, lacked
nematophores and its nematocysts were not examined. As suspected by Hirohoto
(1988), I think that the Japanese E. racemeosum belongs to a separate, unnamed
species. Type locality: Mediterranean, Gulf of Naples, Cave of Gajola, Nisita Island
(now Nisida) and Vico Equano (now Vico Equense) (Cavolini, 1785).
REMARKS: The name Eudendrium racemosum is here attributed to Cavolini
(1785), but one might argue that Cavolini did not use a correct binomial nomen clature.
Although he used indeed the Italian name for the genus (Sertulara), it was clearly used
in a binomial context in the sense of Linnaeus. He treats several recognizable hydroids
which he either assigned to Sertolara or to Tubulara, thus adopting clearly the system
of Linnaeus.
Eudendrium racemosum mucronatum Billard, 1926, a species originally
described from the Suez Canal, does not belong to E. racemosum. Marques et al.
(2000b) re-examined the type specimen and also the other material of Billard. They
found that part of the original material probably belongs to E. carneum, but the holo-
type represents likely a valid species neither referable to E. racemosum nor E. car-
neum. It should thus be used as Eudendrium mucronatum Billard, 1926.
Eudendrium racemosum is one of most common and conspicuous hydroids of
the Mediterranean. It is also relatively easy and reliable to identify due to its isorhiza
capsule, the nematophores, and the branched spadix.
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4699

Eudendrium carneum Clarke, 1882 Fig. 11
Eudendrium carneum Clarke, 1882: 137, pl. 7 figs 10-17. – Fraser, 1944: 64, pl. 8 fig. 36. –
Vervoort, 1968: 8. – Millard, 1975: 82, fig. 28. – Watson, 1985: 202, figs. 59-62. –
Wedler & Larson, 1986: 84, fig. 6Ba-b. – Calder, 1988: 43, figs 33-35. – Bavestrello &
Piraino, 1991: 197, figs 1a-c. – Marinopoulos, 1992: 57, fig. 2.3. – Marques et al., 2000a:
90, figs 35-41. – Marques et al., 2000b: 206.
Eudendrium cunninghami Kirkpatrick, 1910: 127, pl. 7 figs 1-3. – Vannucci, 1954: 101, syno -
nym. – Marques et al., 2000b: 207, synonym.
Eudendrium ramosum. – Weill, 1934b: 388, figs 237. [not Eudendrium ramosum (Linnaeus,
1758)]
MATERIAL EXAMINED: MHNG INVE35472; Honduras, Utila, 16.0687°N 86.9555°W,
depth 20 m; 11 Feb. 2004; fertile female; DNA extracted, 16S DNA sequence accession number
AM991305. – MHNG INVE39470; France, Corsica, Ajaccio; 4 July 1950; male colony. –
ZMUC, without number, as E. ramosum; USA, Cape Cod, Lagoon Pond Bridge; 17 July 1964;
fertile male. – Lebanon; depth 12m; July 2003; male colony; personal collection of Dr S. Puce.
– Lebanon, Beirut Harbour; depth 3m; Sept. 2002; female colony; personal collection of Dr S.
Puce.
DIAGNOSIS: Large, polysiphonic colonies, complementary nematocyst a large
haploneme (anisorhiza); male blastostyles completely atrophied; female blastostyle
completely atrophied or with some few and small tentacle rudiments; female sporosacs
with bifid spadix, during later development reduced but forming a periderm mem brane
holding encapsulated embryos.
DESCRIPTION (Calder, 1988; Bavestrello & Piraino, 1991; own data): Colony ex-
tensively branched and irregularly bushy, arising from a creeping mass of stolons.
Basal part and sometimes also major branches polysiphonic. Perisarc thick, brown in
older parts of colony, thinner and paler towards extremities, annulated or wrinkled at
bases of branches and hydranth pedicels, with occasional annulations elsewhere but
mostly smooth, terminating almost imperceptibly at groove around hydranth base.
Hydranths with large hypostome, up to 32 tentacles.
Male gonophores (>10) in a tuft at end of pedicel, without vestiges of hydranth,
gonophores with 3-4 chambers each, distal end of gonophore with scattered nemato-
cysts.
Female gonophores (4-10) on almost entirely atrophied hydranths, sometimes
transiently with a few reduced tentacles; spadix bifid, curving over egg. After ferti -
lization the spadix is reduced, but before this the spadix secretes a covering of
periderm which then holds the encapsulated embryos in a dense clusters on the
blastostyle pedicels; perisarc membranes often moulded into shape of enlarged spadix,
with two openings, but often also irregular (Fig. 11E).
Nematocysts: microbasic euryteles on tentacles and in other tissues; anisorhizas
with shaft tapering only towards its distal end, thus appearing as isorhiza, scattered on
hydranth base, hypostome, tips of male gonophores.
Colours (Clarke, 1882): hydranths and gonophores red.
DIMENSIONS: Colonies of variable height reaching up to 24 cm (Bavestrello &
Piraino, 1991), more commonly around 10 cm. Hydranths 0.4-0.8 mm total height and
0.5-0.6 mm wide (Bavestrello & Piraino, 1991). Male gonophores 0.5-0.6 mm long,
maximal diameter 0.2 mm; embryo capsules (0.25-0.3)x(0.4)mm. Haploneme
(21-26)x(9-11)μm, r=2.1-2.6; microbasic eurytele (7.5-9)x(3.5-4)μm r=2.3-2.5. Non-
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701
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 11
Eudendrium carneum Clarke, 1882; after preserved Mediterranean material. (A) Colony
silhouette, scale bar 2 cm. (B) Male blastostyle, some terminal chambers have spent their
gametes, scale bar 0.2 mm. (C) Young female blastostyle, same scale as B. (D) More advanced
female blastostyle, note branched spadices, same scale as B. (E) Encapsulated embryos attached
to pedicel of former blastostyle, note fenestrated periderm membranes that hold capsules, same
scale as B. (F) Nematocysts: haploneme and microbasic eurytele. Scale bar 10 μm.

European populations have quite similar values (Millard, 1975; Watson, 1985; Calder,
1988).
BIOLOGY: This species often occurs on ship hulls and is thus potentially easily
introduced to other regions (Millard, 1975). In the Mediterranean, this is not a frequent
species, but along the American coast it can occur in dense stands (Clarke, 1882;
Calder, 1988). It is usually found in depths from 0-20 m (Marques et al., 2000b), but
prefers shady environments (Bavestrello & Piraino, 1991). Fertile colonies have been
found in the Mediterranean from July to December (Marques et al., 2000b; this study).
Detailed ecological studies are provided by McDougall (1943), Wedler (1975), Calder
(1976, 1990). Summers (1972, as E. ramosum) examined the ultrastructure of the
spermatids.
DISTRIBUTION: Mediterranean, perhaps introduced by human activity (Picard,
1958; Bavestrello & Piraino, 1991; Marques et al., 2000b), western Atlantic from New
England to Florida (Fraser, 1944; Marques et al., 2000b), tropical eastern Atlantic
(Vervoort, 1968, Wedler, 1975; Wedler & Larson, 1986), Brazil (Vannucci, 1954),
French Guyana (Bouillon et al., 1995), Island of St Helena (Kirkpatrick, 1910),
southern Africa (Millard, 1959; 1975); western Australia (Watson, 1985), California to
tropical eastern Pacific (Fraser, 1939; 1948), perhaps also Korea (Park, 1991). Type
locality: USA, Virginia, Fort Wool, in the entrance to Hampton Roads (Clarke, 1882).
REMARKS: Although E. carneum has some similarities with E. racemosum (large
colonies, bifid spadix, reduced blastostyles), it can be distinguished rather reliably: its
haplonemes are much larger, mature colonies are always polysiphonic, and the
embryos are held by periderm membranes.
The halplonemes have been variably identified as isorhizas or anisorhizas.
Watson (1985) showed that these capsules have a very long thread (1 mm) which tapers
only in the very terminal region. It is thus easily mistaken for an isorhiza. The
differences between anisorhiza and isorhiza are anyway gradual and often not so clear.
Using the more inclusive term haploneme is thus preferable.
Infertile or male colonies can be mistaken for E. glomeratum if no discharged
nematocysts can be examined. However, E. carneum lacks the characteristic nema -
tocyst buttons of E. glomeratum.
Eudendrium racemosum mucronatum Billard, 1926, a species originally
described from the Suez Canal, does not belong to E. racemosum. Marques et al.
(2000b) re-examined the type specimen and also the other material of Billard. They
found that part of the original material probably belongs to E. carneum, but the
holotype likely represents a valid species neither referable to E. racemosum nor E.
carneum. It should thus be used as Eudendrium mucronatum Billard, 1926.
Eudendrium ramosum (Linnaeus, 1758) Figs 12-14
Tubularia cylindris ramosis Ellis, 1755: 31, pl. 16a, pl. 17A, a.
Tubularia ramosa Linnaeus, 1758: 804.
Tubularia trichoides Pallas, 1766: 84. – Hincks, 1868: 82, synonym.
Eudendrium insigne Hincks, 1861: 160. new synonym
Eudendrium insigne. – Hincks, 1868: 86, pl. 14 fig. 3. – Allman, 1872: 337, pl. 14 figs 4-6.
Eudendrium ramosum. – Hincks, 1868: 82, pl. 13. – Allman, 1872: 332, pl. 13. – Fraser, 1937:
42, pl. 7 fig. 32. – Fraser, 1944: 72, pl. 12 fig. 48. – Yamada, 1954: 27. – Hamond, 1957:
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703
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 12
Eudendrium ramosum (Linnaeus, 1758). (A) Colony, from Ellis (1755). (B) Male gonozooid,
scale bar 0.2 mm, after preserved material from the Mediterranean. (C) Female gonozooid, scale
bar 0.2 mm, after preserved material from the Mediterranean. (D) Nematocysts of Atlantic
material: large microbasic eurytele, same discharged, small tentacular microbasic eurytele.

300. – Naumov, 1969: 266, fig. 135. – Millard & Bouillon, 1973: 32, fig. 31A-D. –
Millard & Bouillon, 1974: 19, fig. 3A-D. – Millard, 1975: 85, fig. 31A-D. – Hirohito,
1988: 87, figs 30d-e, 31a-c, pl. 2 fig. C. – Ramil & Vervoort, 1992: 20. – Marinopoulos,
1992: 59, fig. 5. – Marques et al., 2000a: 104, figs 75-78. – Marques et al., 2000b: 204.
– Schuchert, 2001: 32, fig. 20. – Peña Cantero & García Carrascosa, 2002: 37, fig. 7a-c.
Eudendrium elsae-oswaldae Stechow, 1921: 252. – Stechow, 1923: 81, fig. G. new synonym
Eudendrium elsaeoswaldae. – Marques et al., 2000a: 94, figs 47-49. – in part Marques et al.,
2000b: 209.
? Eudendrium ramosum. – Watson, 1985: 191, figs 29-34.
not Eudendrium ramosum. – van Beneden, 1844. [= Bougainvillia muscus (Allman, 1863)]
not Eudendrium ramosum. – Motz-Kossowska, 1905: 54, pl. 3 fig. 16. [= Eudendrium glome -
ratum Picard, 1952]
not Eudendrium ramosum. – Weill, 1934b: 388, figs 237. [=Eudendrium carneum Clarke, 1882]
not Eudendrium ramosum. – Kramp, 1926: 241. [= Myrionema multicornis (Allman, 1876)]
FIG. 13
(A-C) Eudendrium ramosum (Linnaeus, 1758); native nematocysts of Mediterranean material,
scale bar 10 μm. (A) Large microbasic eurytele. (B) Same discharged. (C) Small microbasic
eurytele.
(D-G) Topotype material of Eudendrium insigne; nematocysts of alcohol preserved material,
scale bar 10 μm. (A) Intact large microbasic eurytele. (B) Same discharged. (C) Small micro -
basic euryteles. (D) Same discharged.
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E. RAMOSUM MATERIAL EXAMINED: MHNG INVE25956; Italy, Naples, 23 Dec. 1891; fe-
male. – MHNG INVE25957; Italy, Naples, coll. 1892, infertile. – MHNG INVE3945; France,
Banyuls-sur-Mer, Cap Abeille; 30 Oct. 1947. – BELUM Md354; Northern Ireland, Strangford
Lough, NW Limestone Rock; 54.421° N 5.611°W; depth 28m; 20 May 1982; female. – BELUM
Md105; Northern Ireland, Strangford Lough, Bay to N of Audley's Point; 54.386°N 5568°W;
depth 12m; 25 April 1976; male. – BELUM, without registration number, field number
900620/01; loc. Ireland; 20 June 1990; male and female colonies. – BELUM, without regis -
tration number, field number 910328/01; Scotland, Sound of Mull, Hispania wreck, depth 18m,
705
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 14
Compementary nematocysts of the syntype material of Eudendrium elsaeoswaldae, ZSM no
20040383, scale bar 10 μm. (A-D) Intact large microbasic euryteles. (E-H) Two discharged large
microbasic euryteles. The image-pairs E+F and G+H depict each the same capsule, but in
different focusing planes, this in order to better visualize the shaft (E, G) or the capsule (F, H).

28 march 1991, male. – ZSM, CT356; Plymouth Zoological Station, coll. 1909; 12cm colony. –
Italy, Portofino, Sept. 2004, depth 15-20m; males; in pers. collection of S. Puce (as E. mou-
louensis). – Italy, Sardinia, Oct. 2005, depth 24m; females; in pers. collection. S. Puce (as E.
moulouensis).
E. INSIGNE MATERIAL EXAMINED: MHNG INVE54560, topotype material for Eudendrium
insigne; England, Torquay, Hope's Nose, rock pool at low water level; 16 June 2007; fertile fe-
male; part used to extract DNA, AM991293. – IRSNB, Ig 11365, as Eudendrium insigne;
Germany, Helgoland, leg. Leloup; female colony of 16 mm. – BELUM Md615; as E. insigne;
Northern Ireland, Strangford Lough Narrows, Rue Point; 54.365°N 5.541°W; depth 25m; 11
Aug. 1983; male. – BELUM Md614; as E. insigne; Northern Ireland; Strangford Lough
Narrows, W of Rue Point; 54.365°N 5542°W; depth 7m; 2 Aug. 1980; female.
E. ELSAEOSWALDAE MATERIAL EXAMINED: Syntype material Eudendrium elsaeoswaldae,
ZSM no 20040383, alcohol and slide preparations, Naples, Posilippo, 20 m.
DIAGNOSIS: Colonies monosiphonic or exceptionally with few complementary
tubes near base; complementary nematocysts large microbasic euryteles with rather
small spines, dispersed on hydranth body. Female and male sporosacs developing on
unreduced hydranths, in later development sometimes partially reduced.
DESCRIPTION: Colonies usually much branched, intertidal colonies can be small,
colony shape slender, elongate with a tendency to pinnate growth (Atlantic popu -
lations); stem usually monosiphonic or occasionally only slightly polysiphonic (2-5
tubes) very close to base. Hydranths with 20-30 tentacles, large euryteles dispersed on
hydranth body, not clustered along basal groove.
Male sporosacs on non-reduced hydranths, up to five per hydranth, two-
chambered; in advanced stages tentacles sometimes atrophied.
Female gonophores develop on normal or slightly smaller hydranths with nor-
mal number of tentacles, up to seven gonophores per gonozooid, spadix simple, long;
gonozooid during later development not or only tentacles atrophied. Encapsulated em-
bryos attached along pedicel.
Nematocysts: small tentacular microbasic euryteles; large complementary
microbasic euryteles, shaft in intact capsule spanning 2/3 to 4/5 of capsule length,
spines on discharged shaft small.
Colours (Allman, 1872): Hydranths reddish; male sporosacs with red spadix;
female gonophores orange-red.
DIMENSIONS: Shoots up to 15 cm high, width usually much less (2-5 cm);
hydranth 0.7-0.8 mm high, diameter 0.4-0.5 mm, pedicel 0.17-0.22 mm. Large micro-
basic euryteles: (13-19.5)x(6.5-9)μm, r=1.9-2.3; small microbasic euryteles (6.5-
8.3)x(2.5-4.3)μm r=2.0-2.5.
VARIATION: The colonies are stout in shallow water and more slender in deeper
waters (Boero & Fresi, 1986). Some Mediterranean colonies had hydranths with
distinct bright bodies (about 30 μm) in their gastrodermis, resembling large cells
densely filled with spherical bodies. They did not stain with iodine and are thus
unlikely to be zoxanthellae. The bodies were seen in the hydranth body, pedicels, and
rarely in the tentacles. It remained unclear whether they are formation of the hydroid
or exogenous, e. g. parasitic protists.
BIOLOGY: The colonies grow on a large variety of solid substrata. Along the
European coasts occurring usually in depths of few metres to about 80 m (Russell,
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1957; Teissier, 1965; Rees & Rowe, 1969; Christiansen, 1972; Peña Cantero & García
Carrascosa, 2002). The fertility period in the Atlantic is at least from March to
November (Allman, 1872; Philbert, 1935; Billard, 1927; Russell, 1957; Teissier, 1965;
Christiansen, 1972). In the Mediterranean, it is present all year round except June, it is
more abundant from October to March; the reproductive period is July to February
(Boero & Fresi, 1986).
DISTRIBUTION: Reportedly circumglobal in warm or temperate waters, also in
the Arctic, but most of the records are doubtful (Marques et al., 2000b). The known
distribution includes the Mediterranean and, all European coasts from the Arctic to
Africa; absent from the Baltic Sea? (Billard, 1927; Leloup, 1947; Rees, 1952; Picard,
1955; Buchanan, 1956; Hamond, 1957; Russell, 1957; Christiansen, 1972; Morri et al.,
1991; Marques et al., 2000a, 2000b; Schuchert, 2001; Peña Cantero & García
Carrascosa, 2002; Vervoort, 2006). Type locality: North Sea, Whitstable, Kent,
England (Boero & Cornelius, 1987).
REMARKS: Eudendrium ramosum is difficult to separate from a number of other
species, notably also E. merulum, E. arbusculum, and E. rameum (Marques et al.,
2000b). When identifying E. ramosum, emphasis must be laid on the monosiphonic or
only lightly fascicled stem base, the dispersed large euryteles on the hydranth body,
and the non reduced gonozooids. The typical colony form was already well depicted
and described by Ellis (1755) (see Fig. 12). These figures served Linnaeus to give it its
present name (hence the figures can be considered as depicting the type specimen).
The diagnosis of Eudendrium insigne Hincks, 1861 is (after Hincks, 1868):
"Colonies 10-20 mm with few branches, monosiphonic, perisarc annulated throughout,
hydranths yellowish-red, male and female gonophores on intact hydranths."
Eudendrium insigne is thus also not readily separable from other Eudendrium
species, particularly E. ramosum, primarily because so far no information on the
nematocysts is available. Searches for type material of E. insigne in several museums
yielded nothing. I therefore tried to collect the species again at its type locality, given
by Hincks as “intertidal, on sponge, Hope's Nose”. Hope's Nose is a rocky promon tory
east of Torquay (Devon, England). When visited in 2007, there were only few suitable
places in the intertidal zone where sponges and hydroids could grow, except for a set
of three small but deep rock pools at low-water level on a quite flat rock platform. At
least two of them harboured dense populations of hydroids, mainly an Aglaophenia
species, but also Coryne muscoides and Campanulariidae. In one of the pools, under-
neath an overhang, several stems of a Eudendrium associated with a sponge were
found. Although we have no idea on how long intertidal rock pools exist over time,
their depth (40 cm) suggests that they could have been present even in Hincks's time
and it is very likely that he collected E. insigne from these three rock pools. The
recently collected Eudendrium stems (MHNG INVE54560) are rather small (up to 10
mm), are branched a few times, have pale orange-red hydranths, the perisarc is exten-
sively annulated but some smooth stretches are present, and the female sporosacs are
on intact or almost intact hydranths. This material thus matches Hincks's description
almost perfectly and it can be assigned to E. insigne without hesitation. The nemato-
cysts proved to be identical to those seen in E. ramosum (Fig. 13). Except for the stem
707
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4

heights, there is thus nothing that distinguishes E. insigne from E. ramosum. The stem
size and the more pronounced annulation, however, can easily be attributed to its origin
in the intertidal, wave-exposed region. Eudendrium insigne Hincks, 1861 must there-
fore be regarded as conspecific with Eudendrium ramosum (Linnaeus, 1758) as defined
here.
Eudendrium elseoswaldae Stechow, 1921 from the region of Naples was
characterized by Stechow (1923) by its long, monosiphonic stems (up to 23 cm) and
the elongated hydranths without perisarc groove. Stechow (1923), who did not have
fertile material, admitted that his material closely resembled Eudendrium ramosum
depicted in Hincks (1868: pl. 13). Later authors (e. g. Picard, 1958; Marinopoulos,
1992; Boero & Bouillon, 1993) implicitly considered the species either a synonym or
doubtful as they did not include it in their lists of the Mediterranean Eudendrium
species. Marques et al. (2000a, 2000b) redescribed the species based on type and non-
material and considered it as a distinct species characterized by the presence of large
atrichous isorhizas. The type material of Eudendrium elsaeoswaldae (ZSM number
20040383) was also re-examined for this study. Although the colonies are rather large
(up to 15 cm), there is nothing that distinguishes this material from Eudendrium
ramosum sensu Hincks. The polyps are not all particularly elongated and those that are
so appear artificially stretched. A perisarc groove is present very low on the hydranth
body. An examination of the nematocysts (slide material and alcohol preserved
material) gave deviant results from those reported by Marques et al. (2000b). The
complementary capsules are clearly microbasic euryteles (Fig. 14A-H) that are indis-
tinguishable from those of E. ramosum. There is thus nothing that distinguishes the
type material of Eudendrium elsaeoswaldae from Eudendrium ramosum auct. Euden -
drium elsaeoswaldae Stechow, 1921 is therefore here synonymized with Eudendrium
ramosum (Linnaeus, 1758). As Marques et al. (2000b) had also other material they
considered to belong to E. elseoswaldae, they have perhaps based their nematocyst
observations on this non-type material.
Perigonimus multicornis Allman, 1876 was attributed to Eudendrium ramosum
by Kramp (1926), but a re-examination of the type material showed that it has macro-
basic euryteles and belongs to the genus Myrionema.
Watson (1985) found cnidophores in her Australian material identified as E.
ramosum. Nematophores have never been found in European E. ramosum and
Watson's material belongs perhaps to a new species.
Eudendrium rameum (Pallas, 1766) Fig. 15
Tubularia ramea Pallas, 1766: 83.
Eudendrium rameum. – Hincks, 1868: 80, frontispiece. – Allman, 1872: 334. – Fraser, 1937: 42,
pl. 7 fig. 31. – Fraser, 1944: 71, pl. 11 fig. 47. – Yamada, 1954: 7, fig. 6. – Naumov, 1969:
264, fig. 133. – Millard, 1977: 3. – Marinopoulos, 1992: 58 fig. 1.6. – Marques et al.,
2000a: 102, figs 71-74. – Marques et al., 2000b: 204. – Schuchert, 2001: 31, fig. 19A-B
– Peña Cantero & García Carrascosa 2002: 35, fig. 7d-e.
Eudendrium planum Bonnevie, 1898a: 483, pl. 26 figs 28-30. news synonym
not Eudendrium planum. – Kramp, 1939: 516. – Calder & Vervoort, 1998: 9, fig. 2a-b. – Kramp,
1932a: 20, figs 9-11, 31. – Schuchert, 2001: 30, fig. 18A-B.
Eudendrium stratum Bonnevie, 1898a: 483, pl. 26 figs 22-24. news synonym
not Eudendrium rameum. – Hirohito, 1988: 84, fig. 30a-c.
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EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 15
Eudendrium rameum (Pallas, 1766), after preserved material from Norway (Trondheim Fjord).
(A) Colony silhouette, scale bar 2 cm. (B) Base of side branch with annulation, same scale as D.
(C) Hydranth with male gonophores, same scale as D. (D) Female gonophores on slightly
reduced hydranth (tentacles shortened), scale bar 0.2 mm. (E) Blastostyle with eggs on partially
reduced hydranth and encapsulated embryos attached to pedicel, same scale as D. (F)
Nematocysts: small microbasic eurytele, large microbasic eurytele, same discharged, scale bar
10 μm.

TYPE MATERIAL EXAMINED: ZMO B1238, syntype colonies of Eudendrium planum,
Zoological museum of Oslo; no locality or date; on label note that also Lafoea serpens and
Campanulina fastigata Alder present. – ZMO B1239, type colony of Eudendrium stratum; no
locality; fragments of polysiphonic colony, with male gonophores.
Other MATERIAL EXAMINED: MHNG INVE33539, BIOFAR station 726; The Faroes,
60.66°N 06.91°W, depth 400m; 29 Sept. 1990, infertile. – MHNG INVE33588, BIOFAR station
554; The Faroes, 61.93°N 6.49°W, depth 62m; 22 Sept. 1989, 2 infertile colonies. – MHNG IN-
VE38221; Mediterranean, France, Marseille, Grotte de Figuier; 24 April 1970; leg. H.
Zibrowius; fertile female. – MHNG INVE49888; Italy, Naples; 21 Jan. 1892; infertile. –
SMNH89692; Norway, SE to S off Bergen, 182-291m; collected ca. 1874; material mentioned
in Jäderholm (1909); no hydranths or gonophores left. – ZSM, Stechow collection, Valdivia
station 3, Aberdeen, Scotland, depth 79m, 57°26'N 1°28'W, det. E. Stechow, without gono -
phores. – ZSM, CT349, Material Bedot Nr. 69, det. E. Stechow, Cap Misano near Naples, 23 Jan.
1892, several colonies, max. 5cm, fertile male. – ZSM, slide 20000794, Naples, fragments of
male and female colony. – ZMUC, without number; Norway, Trondheim Fjord, Vennes; depth
6.5m; 18 Sept. 1934; female and male colonies.
DIAGNOSIS: Colonies large, polysiphonic, usually tree-like with a distinct trunk,
female on hydranth with hypostome, with variably developed tentacles, spadix simple;
male gonophores on normal hydranth which can get somewhat reduced during matu-
ration. Complementary nematocysts a microbasic eurytele, dispersed on hydranth
body, shaft thin, in undischarged capsule spanning 4/5 or more of capsule.
DESCRIPTION: Colonies much branched, stem and branches polysiphonic, ter -
minal branches simple. Colony form usually tree-like with a thick trunk. Hydrorhiza
root-like, creeping. Perisarc thick, short stretches of annulation frequent, especially at
bases of branches. Hydranths typical for genus, without nematocyst buttons or ring,
16-24 tentacles.
Male gonophores on normal, tentacle bearing hydranth which is not or only
slightly reduced after maturation of the gonads, up to 12 gonophores per hydranth, in
dense whorl around body of hydranth, with one to three chambers, without terminal
nematocyst clusters.
Female gonophores (up to 16 per hydranth) develop on hydranths with a hypo-
stome and with shortened tentacles, spadices simple, tentacles get variably reduced:
Fertilized eggs loose spadix and get encapsulated in perisarc membrane and attached
to pedicels of former blastostyle, the latter can resume growth.
Nematocysts: small microbasic euryteles predominantly on tentacles; large
microbasic euryteles, shaft with fine spines, only slightly swollen and sometimes indis -
tinguishable from mastigophores type, shaft in undischarged capsule long, spanning
4/5 to 1/1 of capsule length, discharged shaft about as long or slightly longer than
capsule.
Colours: perisarc brown, hydranths pale.
DIMENSIONS: Colonies 4-20 cm, mostly below 12 cm; hydranths 0.5 mm dia-
meter and total height 0.7-0.8 mm; diameter of hydranth pedicels 0.15-0.2 mm, dia-
meter of basal stem tubes 0.23-0.26 mm. Small microbasic eurytele (7-9)x(3-5)μm, r=
1.8-2.5. Large microbasic eurytele (20-26)x(8-11)μm, r= 2.4-2.8.
BIOLOGY: Mostly recorded in depths from a few metres to about 100 m on hard
bottoms (Christiansen, 1972). There are not enough data on the fertility periods
available. Fertile colonies from the Mediterranean have been found in the months
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January, April, and September (Marques et al., 2000b; this study). For the North Sea,
Hamond (1957) give a fertile period of November to March. In Norway, Christiansen
(1972) observed sporosacs between June and October.
DISTRIBUTION: The species has been recorded in almost all oceans, but only
identifications also using nematocyst morphology can be considered reliable. It is thus
certainly present in the Mediterranean, along the European Atlantic coast, Greenland,
Iceland (Marques et al., 2000a and 2000b; Schuchert, 2001; Peña Cantero & García
Carrascosa, 2002), and southern Indian Ocean (Millard, 1977). Type locality:
Mediterranean (Pallas, 1766).
REMARKS: Pallas (1766) described Eudendrium rameum as a polysiphonic, tree-
like colony which he qualified as common in the Mediterranean ("Locus: Mare
Mediterraneum, præcipue ubi Filigrana Planci abundat"). The species as conceived
today is not common in the Mediterranean and Pallas's diagnosis could either refer to
E. rameum, E. glomeratum, or even E. racemosum. While earlier authors diagnosed
this species mostly through its tree-like colony form, our current scope of the species
relies additionally on the presence of dispersed large microbasic euryteles and on the
unreduced or only moderately reduced blastostyles. However, Marques et al. (2000a)
are right by qualifying this species and E. ramosum as confusing. Preliminary mole -
cular data (Moura et al., 2008 and Fig. 2) indicate that our current concept of E.
rameum comprises several lineages and perhaps also several species.
The type specimens (2 colonies plus some fragments) of Eudendrium planum
Bonnevie, 1898a were examined for this study. The stems are up to 6 cm high, strong -
ly polysiphonic. The colonies are female, only encapsulated embryos attached to
blastostyle pedicels are present. There are no gonophore stages with spadices. The
arrangement is in no way particular. As nematocysts there are two types of microbasic
euryteles, small almond-shaped (7-8)x(3)μm (tentacular type) and large elongate oval
ones sized (16-19)x(6-7)μm, r=2.5-3.2. The shaft in the intact larger eurytele spans
almost the whole length of the capsule. All these data match perfectly our current
concept of Eudendrium rameum. Eudendrium planum should therefore be regarded as
a synonym of the former species. Calder, & Vervoort (1998) and Schuchert (2001) also
described nematocysts of tentatively identified E. planum. Both studies found macro-
basic euryteles, meaning that these specimens are neither E. planum nor E. rameum.
The specimen of E. planum described by Kramp (1939; Kara Sea; kept by ZMUC) has
differently shaped complementary capsules (with pointed ends) without a visible shaft
inside. Also this record is thus not E. planum, more likely it is an undescribed species.
Together with E. planum, Bonnevie (1898a) also described Eudendrium stra-
tum. She characterized this species by the peculiar covering of the stem. The type spe-
cimen was re-examined for this study. It consists of several polysiphonic stem frag-
ments. Male gonophores with 3 chambers are present on unreduced hydranths. The
stem is covered by a soft tissue with a spongy, cellular structure containing no nema-
tocysts. It is unclear what this covering is, but is very unlikely that it was produced by
the hydroid and it must be foreign. The nematocysts of the hydroid appear identical to
E. planum, though somewhat larger. The complementary capsules are likely hetero -
nemes (none seen discharged) with a size of (20-22)x(9-10)μm. The apparent shaft is
711
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4

often not well visible, but when visible, it spans the entire length of the capsule,
sometimes it is even somewhat curved. There are no traits visible in this material that
would preclude its identification as E. rameum as defined here. Eudendrium stratum
is therefore regarded as a synonym of E. rameum.
Eudendrium moulouyensis Marques, Peña Cantero & Vervoort, 2000 Figs 16-19
? Eudendrium hargitti. – Castric & Michel, 1982: 82, fig. [not Myrionema hargitti (Congdon,
1906)]
Eudendrium moulouyensis Marques, Peña Cantero & Vervoort, 2000: 200, fig. 1. – Peña Cantero
& García Carrascosa 2002: 31. – Puce et al., 2005: 202, fig. 1e, 2l-m. – De Vito et al.,
2008: in press.
MATERIAL EXAMINED: MHNG INVE49716; Mediterranean, Spain, Mallorca, Cala
Murada, depth 4m, 20 Aug. 1999; female and male colonies on roots and old leaves of Posidonia
oceanica. – Italy, Calabria, Punta Palascìa, depth 10-15m, 19 Aug. 2004, infertile colonies;
private collection of D. De Vito. – Italy, Calabria, Punta Palascìa, depth 10-15m, 8 Nov. 2006,
infertile colonies; private collection of D. De Vito. – Italy, Calabria, Punta Facì, depth 5-10 m,
14 Dec. 2004, female and male colonies; private collection of D. De Vito.
DIAGNOSIS: Colonies branched, gastrodermis with numerous zooxanthellae,
complementary nematocysts large microbasic euryteles, male blastostyle normal
hydranth, female gonophores on hydranth with shortened tentacles.
DESCRIPTION: Colonies erect, branched, mostly monosiphonic, sometimes stem
base moderately polysiphonic (2-4 tubes), perisarc smooth, occasional annulated
stretches especially near origin of branches. Gastrodermis of coenosarc and hydranths
contains zooxanthellae (Fig. 17), density variable, some hydranths may have only few
zooxanthellae. Hydranths with one whorl of 25-30 tentacles, scattered large euryteles
on hydranth body. Epidermis of hydranths often, but not always, with spumous
inclusion bodies (Fig. 18D), especially between tentacle bases.
Male blastostyles develop as normal hydranths, not reduced when mature, with
up to 10 sporosacs per hydranth, sporosacs two-chambered, with scattered euryteles,
without terminal nematocyst button.
Female sporosacs develop concomitantly with hydranth bearing them, the latter
remains usually somewhat reduced, the size small and the tentacles short; spadix
simple, with scattered large euryteles; fertilized eggs encapsulated and attached to
perisarc of blastostyle pedicels. Nematocysts: small and large microbasic euryteles.
Colour: gastrodermis brownish due to zooxanthellae.
DIMENSIONS: Colonies up to 4 cm high; hydranths 0.5-0.75 mm high and 0.35
mm wide; pedicel diameters 0.1-0.16 mm. Small microbasic euryteles (7-8.5)x(3-
3.5)μm, r=2.1-2.8. Large microbasic euryteles (13-17)x(6-8.5), r= 1.9-2.6. Diameter of
zooxanthellae 8.5-13 μm.
BIOLOGY: Occurs in shallow waters from about 1 to 15 m.
DISTRIBUTION: Mediterranean, perhaps also southern Brittany (Castric et al.,
1987, as Eudendrium hargitti). Type locality: Mediterranean Sea, Morocco, Chafarinas
Islands.
REMARKS: Except for the zooxanthellae, this species resembles closely – or is
indistinguishable – from Eudendrium ramosum. Some colonies from Calabria even
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EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 16
Eudendrium moulouyensis Marques, Peña Cantero & Vervoort, 2000, after preserved material.
(A) Colony silhouette, scale bar 1 cm. (B) Nematocysts: undischarged large and small micro -
basic euryteles, scale bar 10 μm. (C) Developing female blastostyle, scale bar 0.2 mm. (D) More
advanced female blastostyle, same scale as C. (E) Mature female blastostyle, same scale as C.
(F) Mature male gonozooid, same scale as C.

had a moderately polysiphonic stem base, thus reinforcing the similarity. The density
of the zooxanthellae is variable, while some hydranths have only few, others of the
same colony may have many. The density is also variable between colonies.
Several samples had conspicuous white inclusion bodies in the epidermis, espe-
cially between the tentacle bases. They are easily visible in living and preserved
material as white spots. Under the microscope, these bodies look like spumous cells
(Fig. 18D). The content does not react with iodine, thus it contains no starch, nor is it
calcareous as it does not react with lactic acid. Not all colonies have them. Identical
spumous bodies were also found in some E. ramosum. It is not clear what these
inclusions are; perhaps they are parasitic protists.
Castric et al. (1987) depict a zooxanthellae containing Eudendrium they iden -
tified as Eudendrium hargitti. Although they give not enough details, the depicted
microbasic eurytele matches E. moulouyensis rather than Myrionema hargitti (=M. am-
boinense) which has macrobasic euryteles. Eudendrium moulouyensis thus likely also
occurs along the southern coasts of Brittany.
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714
FIG. 17
Eudendrium moulouyensis Marques, Peña Cantero & Vervoort, 2000; hydranth with stained
zooxanthellae (iodine reaction); scale bar 0.1 mm.

Eudendrium cf. merulum Watson, 1985 Figs 19-20
Eudendrium merulum Watson, 1985: 200, figs 53-58. – Bavestrello & Piraino, 1991: 200, figs 2-
4. – Marques et al., 2000a: 100, figs 64-66. – Marques et al., 2000b: 203. – Peña Cantero
& García Carrascosa, 2002: 30, fig. 5a-b. – Bouillon et al., 2004: 59, fig. 35A-G.
MATERIAL EXAMINED: MHNG INVE49879; Black Sea, Bulgaria, Varna, St. Constantine
and Helena yacht port; 1 m; 17 Aug. 2003; female colonies. – MHNG INVE49880; Bulgaria,
Varna, St. Constantine and Helena yacht port; 1 m; 14 July 2003; female and male colonies. –
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EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 18
Eudendrium moulouyensis Marques, Peña Cantero & Vervoort, 2000, microscopic preparations
of preserved material from Otranto, scale bar 10 μm valid for all sections. (A-B) Undischarged
large euryteles. (C) Small microbasic euryteles. (D) Undischarged large euryteles and a spumous
inclusion body (centre).

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716
FIG. 19
Eudendrium cf. merulum Watson, 1985; A-C after preserved material from the Black Sea, D after
Mediterranean material. (A) Colony silhouettes, scale bar 1 cm. (B) A small male blastostyle,
note that they can be larger and comprise twice as many sporosacs; scale bar 0.2 mm. (C) Female
blastostyle, some gonophores at early stages of development, short tentacles are present; same
scale as B. (D) Male sporosac in semitransparent view, note terminal button with a few nema -
tocysts; scale bar 0.1 mm, (E) Nematocysts: small microbasic euryteles, undischarged and
discharged large microbasic eurytele, note the prominent spines; scale bar 10 μm.

MHNG INVE55454; Black Sea, Bulgaria, Varna, St. Constantine and Helena yacht port; 1 m;
30 July 2007; female and male colonies; 16S DNA sequence accession number of one male stem
AM991291. – MHNG INVE55455; Bulgaria, Varna, St. Constantine and Helena yacht port; 1
m; 25 July 2007; female and male colonies; 16S DNA sequence of one male colony identical to
AM991291. – Italy, Otranto, Punta Facì; 5-10 m; 25 July 2005; infertile; pers. collection D. De
Vito. – Italy, Otranto, Punta Facì; 1-5 m; 23 July 2004; infertile; pers. collection D. De Vito. –
English Channel, France, Normandy, Cotentin Penisula, Agon; depth 0 m; 20 Aug. 2005; small
infertile monosiphonic colonies on sponge; material not preserved, all used for nematocyst exa-
mination and DNA extraction; 16S DNA sequence accession number AM991300. – Atlantic,
Spain, Cantabria, Noja, Playa de Ris, depth 0-2 m; 19 Jul. 2003; small stolonal colony on
sponge, male blastostyles completely reduced, large (24μm) supplementary microbasic eury teles
with thick shaft; material not preserved, all used to make DNA, 16S DNA sequence identical to
AM991300. – MHNG INVE27670, as Eudendrium cf. merulum; Canary Islands, Tenerife,
Radazul, 20-30 m; 2 Oct. 1999; male and female colonies.
DIAGNOSIS: Colonies branched, monosiphonic, cnidome comprises large micro-
basic eurytele having a thick shaft and large spines; male blastostyle completely
reduced, gonophores without terminal button; female blastostyles reduced hydranth
with rudimentary tentacles and without hypostome.
DESCRIPTION: Colonies erect, branched, monosiphonic, arising from creeping
stolons. Stems with up to 15 hydranths, rarely more; perisarc with smooth, corrugated,
or annulated stretches. Hydranths as typical for genus, 16-24 tentacles; basal grove
near proximal end, large nematocysts scattered on hydranth body, sometimes concen-
trated in indistinct band above basal grove.
Male blastostyles completely reduced, sporosacs as tuft at end of pedicels, 1-2
chambered, rarely a third smaller proximal chamber present, connection between
chambers thick, without distinct neck, terminal nematocyst button with some large
euryteles can be present in mature sporosacs.
Female blastostyle small, reduced hydranth without hypostome, with few
tentacle rudiments, about 4-6 sporosacs per blastostyle; sporosacs with simple, curved
spadix. Fertilized eggs encapsulated in thin perisarc membrane and attached to blasto -
style pedicels.
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EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 20
Eudendrium cf. merulum Watson, 1985; complementary microbasic eurytele of colony from the
English Channel. Length of undischarged capsule 21-23 μm, magnifications of A and B are not
identical. (A) Undischarged capsule. (B) Same discharged.

Nematocysts: small microbasic euryteles occurring predominantly on tentacles;
large microbasic euryteles, shaft of undischarged capsule spanning 3/5 of capsule and
rather thick, discharged shaft also thick and with strong swelling, with numerous and
strong barbs, thread relatively thick and also barbed.
Colours (Bavestrello & Piraino, 1991); hydranths are whitish.
DIMENSIONS: Stems usually up to 2 cm, diameter of hydranth pedicels 0.18-0.2
mm, hydranths 0.45-0.6 mm from groove to mouth, stem diameter at base 0.15 mm.
Small microbasic euryteles (6-8)x(2.5-4)μm, r= 2-2.8; large microbasic euryteles
(18-26)x(9-13.5)μm, r= 1.8-2.4 (nematocyst measured in preserved material).
BIOLOGY: Occurs in depths of 1-15 m. In the Mediterranean and Black Sea it
grows on rocks, barnacles and other solid substrata, gonophores were observed from
January to August. The Atlantic colonies grew on sponges and other substrates.
DISTRIBUTION: Australia (Watson, 1985); Yemen (Marques et al., 2000a);
western and eastern Mediterranean (Bavestrello & Piraino, 1991; Marques et al.,
2000b; Peña Cantero & García Carrascosa, 2002); Black Sea (new record); Canary
islands, Gulf of Biscaya and English Channel (new records, but see below). Type lo-
cality: Bass Strait, Victoria, Australia.
REMARKS: Eudendrium merulum as conceived by Marques et al. (2000b) and
also the present paper resembles E. ramosum, but has completely or strongly reduced
blastostyles. The shaft of the large microbasic euryteles of E. merulum also differs in
being much thicker and in having large spines (comp. Figs 13 and 19E). Marques et al.
(2000b) state that the male sporosacs have a narrow connection between the succes sive
chambers. This was not found in the material examined in this study.
Some available 16S sequence data (publication in preparation, see also Fig. 2)
indicate that the Atlantic, Mediterranean, and Black Sea populations here attributed to
E. merulum belong to at least three unrelated lineages, likely representing three
different biological species. As it is likely that they are also distinct from the Australian
E. merulum, the species as currently perceived is certainly a species complex and it was
here therefore listed as Eudendrium cf. merulum only.
Eudendrium merulum was originally described based on material from southern
Australia, where it is a rather rare species (J. Watson, pers. com.). Bavestrello &
Piraino (1991) then found several Mediterranean colonies that matched the diagnosis
of E. merulum. Later also Marques et al. (2000b) described additional Mediterranean
material. The referral to the European material to the Australian E. merulum is some-
what arbitrary, it could as well have been attributed to E. kirkpatriki Watson, 1985. This
is especially true for the material seen in this study which had female blastostyles with
some tentacle rudiments. In the previously described specimens, the female blasto -
styles were completely atrophied. However, the presence of rudimentary tentacles on
the blastostyles is often only transitory and their presence/absence falls within the
intraspecific variation observed in other species. Other observed slight differences to
the description of Watson (1985) and Bavestrello & Piraino (1991) concern the male
gonophore: they have 1-2 chambers instead of 2-3, lack the thin neck between them,
and have an occasional terminal button with some euryteles. All these small dif ferences
are thought to be insignificant, or in current taxonomic practice they are considered at
P. SCHUCHERT
718

least insufficient to separate different species. The material from the Canaries was
particularly difficult to evaluate and differed from the other samples, but without
showing acceptable diagnostic traits that would have allowed diagnosing it as a distinct
species. The colonies were much larger (10 cm, mostly monosiphonic, shape resem-
bling E. ramosum), the stem diameter was much thicker than in the other E. merulum
(0.34 mm), the hydranths were larger (0.7 mm), the spadix longer with a tendance to
form a spiral, and the large euryteles were larger (25-30 μm long) and they were
concentrated in an indistinct band near the basal groove. The colonies appeared thus
intermediate between E. ramosum and E. arbuscula.
Eudendrium merulum is part of the E. ramosum group, which comprises several
Eudendrium species with a large complimentary eurytele and which are often not
reliably identifiable (see also Marques, 1995). It is unlikely that detailed morpho logical
analyses of allopatric populations can provide us with reliable species diagnoses.
Useful diagnostic features might become more evident only after a DNA analysis will
have provided us with a robust phylogenetic tree of the species.
Eudendrium annulatum Norman, 1864 Figs 21-24
Eudendrium annulatum Norman, 1864: 83, pl. 9 figs 1-2. – Hincks, 1868: 83, pl. 15 fig. 1. –
Allman, 1872: 339. – Bétencourt, 1899: 4, pl. 1 figs. 1-4. – Bonnevie, 1898a: 482, pl. 26
figs 31-33. – Broch, 1910: 201. – Broch, 1916: 62, fig. T. – Fraser, 1944: 62, pl. 7 fig.
33. – Christiansen, 1972: 289.
in part Eudendrium annulatum. – Jäderholm 1909: 51, pl. 4, figs 3-4. – Naumov, 1969: 265, fig.
134.
not Eudendrium annulatum. – Leloup, 1940: 5, 29. –Yamada, 1954: 2, text-fig. 1.
not Eudendrium annulatum. – Schuchert 2001: 26, fig. 15A-C. [=E. vaginatum Allman, 1863]
Eudendrium cf. arbuscula. – Schuchert, 2001: 33, fig. 21. [not Eudendrium arbuscula Wright,
1859]
TYPE MATERIAL EXAMINED: BMNH 1898.5.7.40; syntypes of Eudendrium annulatum
Norman, 1864; Shetland Isles, Burrafirth Caves, "Burness Hall"; coll. 1863; 2 infertile colonies,
one colony likely depicted in Norman (1864). – RMNH Coel28436, syntype (slide preparation);
Great Britain, Shetland, Burrafirth Caves, "Burness Hall".
OTHER MATERIAL EXAMINED: BELUM Md363; Scotland, Outer Hebrides, Scarba, NE
Rubh A Chuil; 56°11.96'N 05°41.30'W; 27 m; 12 July 1982; infertile. – BELUM Md628;
Scotland, Outer Hebrides, St. Kilda, NE of Stac Lee; 57°52.01'N 08°30.45'W; 25 m; 9 July 1984;
infertile. – BELUM Md421; Scotland, Outer Hebrides, Scarba, Bealach a Choin Glais (Grey
Dogs Race); 56°12.50'N 05°41.70'W; 17 July 1982; infertile. – BELUM Md108, as E. ramosum;
Northern Ireland, Donegal, south side of Rathlin O'Birne; 54°22.38'N 05°33.15'W; 30m; 21 Nov.
1976; fertile females and males. – BELUM Md109; Northern Ireland, Donegal, Torneady Point;
55°01.51'N 08°32.43'W; 36 m; 8 April 1978; infertile. – BELUM Md629; Northern Ireland,
Antrim, Rathlin Island, NE of Farganlack Point; 55°18.74'N 06°15.06'W; 24m; 7 July 1984; in-
fertile. – BELUM Md630; Northern Ireland, Antrim, Maidens, W Side of The Bushes;
54°55.38'N 05°43.84'W; 25m; 25 July 1983; infertile.
DIAGNOSIS: Large polysiphonic colonies, stems with bark-like covering,
hydranths large (>0.4 mm diameter), usually with basal ring of large microbasic eury-
teles, blastostyles aggregated on upper side of branches, their pedicels relatively short,
gonophores with distal nematocyst buttons.
DESCRIPTION: Colonies large, stiff, rather stout and coarse, stems and branches
polysiphonic, typically with rather elongate stem or primary branches provided with
shorter side-branches resembling somewhat a bottle-brush (Fig. 21A). Stem and
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EUROPEAN ATHECATE HYDROIDS, FILIFERA 4

thicker branches often covered by a smooth layer of coalesced stolonal tubes forming
a dense-meshed, bark-like covering (Fig. 23). Perisarc of branches brown, thick, with
smooth stretches and some annulated or corrugated stretches. Hydranths large, 16-22
tentacles, on body a broad band densely beset with large euryteles, these may be
missing or inconspicuous in some colonies; basal groove marked, near base of body,
filmy perisarc originating in basal groove sometimes loose and forming a short perisarc
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720
FIG. 21
Eudendrium annulatum, after preserved material from Northern Ireland. (A) Colony silhouettes
showing typical colony form, scale bar 1 cm. (B) Typical hydranth, note broad band of nemato-
cysts on body, no perisarc collar present, scale bar 0.2 mm. (C) Terminal branchlet and hydranth
base with short, filmy perisarc collar, same scale as B. (D) Nematocysts: small microbasic eury-
teles, large microbasic eurytele, large eurytele discharged.

collar (Fig. 21C). Colonies dioecious, blastostyles on short pedicels, often in dense ag-
gregates on upper side of distal, monosiphonic hydrocladia (Fig. 24).
Male gonophores are formed in tufts at the end of short branchlets (Fig. 22A),
hydranths absent at all stages of development, distal ends of sporosacs with numerous
large eurytele capsules, mature gonophores 1-2 chambered, when two-chambered both
chambers equivalent, terminal nematocyst button nearly always present (Fig. 22B).
Female gonophores develop like male ones at end of branchlets, eggs present at
early stage, curved spadix beset with euryteles, during later development some
transient, very short tentacle rudiments may form (Fig. 22C-D) that are later lost.
Nematocysts: small microbasic euryteles in tentacles; larger microbasic eury -
tele, relatively rounded capsule, shaft in intact capsule ca. 3/4of capsule length, dis -
charged slightly longer than capsule, directed obliquely, distinctly swollen and with
coarse spines, unambiguously identifiable as eurytele. Colours: perisarc brownish,
hydranths white.
721
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 22
Eudendrium annulatum, after preserved material from Northern Ireland. (A) Developing male
blastostyle, note presence of large euryteles at the tips of the developing gonophores, same scale
as B. (B) Mature male blastostyle, scale bar 0.2 mm. (C) Developing female blastostyle, in the
gonophore at right an immature egg is visible, same scale as B. (D) Slightly more advanced
female blastostyle than shown in C, the spadices with euryteles curve over immature eggs, some
tentacle rudiments with large euryteles are visible at the top, same scale as B.

DIMENSIONS: Colony height 4-10 cm. Hydranth diameter below tentacles
0.35-0.57 mm, height from basal groove to mouth 0.5-0.6 mm. Diameter of hydranth
pedicels 0.18-0.24 mm. Small eurytele (8-9.5)x(3.5-4.5)μm, r= 2-2.7. Large eurytele
(15-17)x(6.5-7.5)μm, r= 2.1-2.5.
BIOLOGY: Insufficient data on fertility periods are available, perhaps fertile
during autumn and winter (comp. examined material; Bétencourt, 1899).
DISTRIBUTION: North Atlantic, boreal to Arctic regions (Norman, 1864;
Levinsen, 1893; Bonnevie, 1898a; Broch, 1910, 1916; Fraser, 1944; Naumov, 1969;
Christiansen, 1972). The southernmost trustworthy record is by Bétencourt (1899) for
P. SCHUCHERT
722
FIG. 23
Eudendrium annulatum, type colony, bark-like overgrowth on stem.

the English Channel, although he had beached material only. There are also several
unreliable records. Type locality: Shetland Isles, Burrafirth, Bunness Hall cave, depth
0.3 m below ELWS.
723
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 24
Eudendrium annulatum, preserved material from Northern Ireland showing male blastostyles in
dense stands on upper side of hydrocladium.

REMARKS: The epithet of E. annulatum is misleading. Neither the type material
nor the other samples from Scotland and Ireland are extensively annulated. There are
annulated stretches at the origin of branches and some hydranth pedicels are entirely
annulated, but most of the perisarc is smooth. The suggestive name has occasionally
led other authors to use it for species with a complete annulation like E. ritchiei (see
e.g. Millard, 1975).
Eudendrium annulatum has been synonymized with E. vaginatum Allman, 1863
by Marques et al. (2000a), but this is incorrect (see discussion under E. vaginatum).
It has so far been ignored that E. annulatum has usually a belt of nematocysts
on the hydranth body and that it has male gonophores with terminal nematocyst but-
tons (Figs 21B, 22A-B). It resembles thus closely E. arbuscula Wright, 1859 with
which it also shares the same nematocysts and the characteristics of the blastostyles.
However, both species appear to be distinct and their differences are given under E. ar-
buscula and in the key to the species. The belt of nematocysts can apparently be absent
in some specimens. In the syntype material, only one colony of the two had such a belt.
The material from Spitsbergen identified by Leloup (1940) as E. annulatum was
re-examined for this study (IRSNB IG12981). It is a small Eudendrium, originally
growing on Halecium muricatum, and it does unlikely belong to E. annulatum. The
state of the material does not allow a reliable identification, but it resembles E. ca-
pillare.
Eudendrium arbuscula Wright, 1859 Figs 25-27
not Tubularia arbuscula D'Orbigny, 1846.
Eudendrium arbuscula Wright, 1859: 113, pl. 9 figs 5-6.
Eudendrium arbusculum. – Hincks, 1868: 84, pl. 14 fig. 1. – Calder, 1972: 225, pl. 2 fig. 5.
Eudendrium arbuscula. – Allman, 1872: 336. – Bonnevie, 1899: 50. – Broch, 1928: 113. – Weill,
1934a: 77, fig 70a-b. – Weill, 1934b: 386, fig. 236. – Castric & Michel, 1982: 82, fig. –
Marques & Vervoort, 1999: 16. – Marques et al., 2000b: 81, figs 11-15. – ICZN, 2000:
180-181. – Faasse & Vervoort, 2005: 61, fig. 4, photos 4, 7, 8.
Eudendrium rigidum Allman, 1876: 253, pl. 9 figs 3-4. – Kramp 1926: 242, synonym.
Eudendrium wrightii Hartlaub, 1905: 547, new name.
? Eudendrium caricum Jäderholm, 1908: 5, pl. 1 fig. 4, pl. 2 fig. 1. – Calder, 1972: 225, synonym.
Eudendrium wrighti. – Broch, 1916: 60, map. T.
not Eudendrium arbusculum. – Hamond, 1957: 300, figs. 7, 8.
not Eudendrium arbuscula. – Marinopoulos, 1992: 58, fig. 1.8.
not Eudendrium cf. arbuscula. – Schuchert, 2001: 33, fig. 21. [= E. annulatum]
TYPE MATERIAL EXAMINED: ZMUC; syntype material of Eudendrium rigidum Allman,
1876; Denmark, Middelfart Sund; infertile; leg. Lütken, compare Kramp (1926: 242). – BMNH
1912.12.21.98; ?syntype of Eudendrium rigidum Allman, 1876; Denmark; infertile.
OTHER MATERIAL EXAMINED: ZMUC, as Eudendrium wrighti; Denmark, off Treindelens
Lightship; 27 Jul. 1904; infertile. – ZMUC, as Eudendrium wrighti; Denmark, Little Belt; depth
16-20m; 26 March 1915; infertile. – BELUM Md424; 55° 13.51'N 06° 38.97'W; Northern
Ireland, Antrim, NW of Little Skerry Potrush; depth 36m; 03 Aug. 1982; infertile. – BELUM
Md492; 54°23.39'N 05°34.64'W; Northern Ireland, Down, Strangford Lough, Ballyhenry Island;
depth 25m; 30 June 1982; infertile. – BELUM Md624; 54°41.66'N 05°47.15'W; Northern
Ireland, Antrim, Belfast Lough, SE of Carrickfergus; depth 7.5m; 15 May 1984; infertile. –
BELUM Md627; 55°08.82'N 07°04.95'W; Northern Ireland, Londonderry, Lough Foyle, East
Channel; depth 7.5m; 22 June 1983; infertile. – BELUM Md626; 51°30.04'N 09°17.70'W;
Ireland, Cork, Lough Hyne, E Whirlpool Cliff; 31 Aug. 1974; infertile. – BELUM Md625;
51°26.90'N 09°49.45'W; Ireland, Cork, SW of Mizen Head; 16 July 1983; infertile. – BELUM
P. SCHUCHERT
724

725
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 25
Eudendrium arbuscula Wright, 1859, after preserved material from Northern Ireland. (A-C)
Colony silhouettes, scale bar 2 cm. (D) Hydranth with nematocyst belt, scale bar 0.2 mm. (E)
Perisarc of branch, same scale as B. (F) Nematocysts: undischarged and discharged small and
large euryteles, scale bar 10 μm.

Md535; 57°57.79'N 05°31.30'W; Scotland, Outer Hebrides, Summer Isles, W Priest Island; 7
Sept. 1981; fertile male. – RMNH-Coel 30986; The Netherlands, Zeeland, Goesse Sars; 15 Nov.
2003; female colonies. – RMNH-Coel 30985; The Netherlands, Zeeland, Zeelandbrug-Noord; 9
Oct. 2004; male colonies. – RMNH-Coel 30983; The Netherlands, Zeeland, Zeelandbrug-
Noord; 8 Oct. 1998; male colonies. – RMNH-Coel 30992; The Netherlands, Zeeland,
Zeelandbrug-Noord; 9 Oct. 2004; female colonies.
DIAGNOSIS: Colonies polysiphonic, much branched, up to 6 cm, stems without
bark-like covering, hydranths small (<0.3 mm diameter), with basal belt of microbasic
euryteles, blastostyles dispersed, without hydranths, gonophores with distal nema -
tocyst buttons.
DESCRIPTION: Colonies bushy, irregular, much branched, usually with numerous
terminal branches and rather dense, either with a rather short basal trunk or no clear
trunk but several main branches issuing from hydrorhiza, polysiphonic, thinning out to
monosiphonic terminal branches, in polysiphonic parts tubes usually rather loosely and
irregularly aggregated and not neatly parallel; perisarc with smooth, corrugated and
annulated stretches, never annulated throughout. Stem not covered by bark-like
covering of coalesced stolonal tubes.
Hydranths relatively small, 16-25 tentacles, on body a broad, dense belt of large
euryteles, basal groove faint, near base of body (Fig. 25D). Colonies dioecious,
blastostyles dispersed over colony.
Male gonophores develop in tufts at the end of branchlets (Fig. 26A), hydranths
absent at all stages of development, distal end of sporosacs with numerous large
euryteles, mature gonophores one-chambered, sometimes a second proximal swelling,
rarely a second chamber, terminal nematocyst button nearly always present.
Female gonophores develop at the end of branchlets (Fig. 26B), concomitantly
with gonophores a small hydranth develops, it has only a small body, short tentacles
stumps, and no hypostome; at later stages it may be reduced entirely; curved spadix
with nematocyst buttons containing large euryteles; after fertilization spadix reduced,
embryos encased in thin membrane and several ones attached along pedicels of former
blastostyles.
Nematocysts: small microbasic euryteles in tentacles; large microbasic eury -
teles, shaft in intact capsule ca. 3/4of capsule length, discharged slightly longer than
capsule, directed upwards, distinctly swollen and with coarse spines, unambiguously
identifiable as eurytele.
Colours: perisarc light brownish, hydranths white or rose-orange.
DIMENSIONS: Colonies 2-6 cm. Hydranth diameter below tentacles 0.17-0.3 mm;
height from basal groove to mouth 0.28-0.5 mm; hydranth pedicel diameter 0.10-0.12
mm. Small euryteles (7-8.5)x(2.5-3.5)μm, r= 2.3-2.5. Large euryteles (14-17)x(6-
7.5)μm r=2.1-2.7.
BIOLOGY: Occurs in rather shallow depths down to about 40 metres. Faasse &
Vervoort (2005) found fertile colonies only during wintertime.
DISTRIBUTION: From Brittany to Norway, also North Sea (Jäderholm, 1909;
Broch, 1916; Kramp, 1942; Rees & Rowe, 1969; Christiansen, 1972; Castric et al.,
1987; Marques et al., 2000a; Faasse & Vervoort, 2005); more frequent along the
P. SCHUCHERT
726

Danish and Irish coast; perhaps also Portugal (Da Cunha, 1944) and NW Atlantic
(Calder, 1972). Due to the unclear synonymy the distribution patter is not well known.
The Mediterranean records (e. g. Marinopoulos, 1992) are likely misidentifications.
Type locality: Queensferry (close to Edinburgh), Firth of Forth, Scotland.
REMARKS: Because Tubularia arbuscula D'Orbigny, 1846, an indeterminate
species, is perhaps referable to the genus Eudendrium, Hartlaub (1905) proposed the
new name Eudendrium wrightii for E. arbuscula Wright, 1859. Following the propo-
sal of Marques & Vervoort (1999), the International Commission of Zoological
Nomenclature (2000) decided that the name Eudendrium arbuscula Wright, 1859
(Cnidaria, Hydrozoa) is to be conserved and placed it on the list of the official names.
The spelling of the specific epithet is arbuscula as it is a noun in apposition (Marques
& Vervoort, 1999).
Unfortunately, no type material of Eudendrium arbuscula could be located, it
must be considered as lost. Eudendrium arbuscula Wright, 1859 was initially charac-
terized (Wright, 1859b) by the broad band of nematocysts on the hydranth body and
the terminal nematocyst button of male sporosacs. Wright's description does not permit
to distinguish it with absolute certainty from E. annulatum as conceived here.
However, as Wright describes the branches as very slender and depicts male sporosacs
with one chamber, it can be excluded with reasonable probability that his material
belonged to E. annulatum Norman, 1864. The present scope of Eudendrium arbus cula
is thus almost certainly correct.
Eudendrium arbuscula nonetheless resembles E. annulatum, notably they share
the same nematocysts, the polysiphonic colonies, the belt of euryteles on the hydranth,
the terminal nematocyst buttons of the gonophores, and the type of blastostyles. They
differ in characters that are usually regarded as taxonomically quite unreliableand and
both could arguably be regarded as only two different forms of the same species.
727
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 26
Eudendrium arbuscula Wright, 1859, blastostyles after preserved material from Holland, scale
bars 0.2 mm. (A) Male sporosacs, note terminal button with nematocysts. (B) Female sporosacs

However, material of both species from the same region (Northern Ireland) was stri-
kingly distinct when compared side by side. The colony forms differ (comp. Fig. 21A
and 25A), Eudendrium annulatum forms more open, coarse, and rather stiff colonies.
The main branches are often covered by a bark-like overgrowth, which is diagnostic for
E. annulatum when present. The hydranths of E. annulatum are distinctly larger, the
diameters are nearly twice as large as those of E. arbuscula. Another difference is the
distribution of the blastostyles, which occur in dense stands on the upper side of distal
branches in E. annulatum, while they are not so regularly grouped in E. arbuscula
(based on rather few observations, difference may be due to limited number of obser-
vations). The pedicels of the blastostyles of E. annulatum are relatively short.
Eudendrium rigidum Allman, 1876, based on infertile material from Denmark,
was synonymized with E. arbuscula by Kramp (1926). The type material of E. rigidum
was also examined for this study and the results confirmed Kramp's findings.
The Greenlandic material identified by Schuchert (2001) as Eudendrium cf.
arbuscula had stems with a bark-like covering, which is found only in E. annulatum
and E. vaginatum. Colony size and form matched E. annulatum and the material is
therefore here re-assigned to the latter species.
Calder (1972) proposed that also Eudendrium caricum Jäderholm, 1908 could
be a synonym of E. arbuscula. Due to the similarity of E. annulatum, the type material
of Eudendrium caricum should be re-examined to prove this possibility.
Hamond's (1957) material identified as E. arbuscula unlikely belongs to this
species. The colonies were rather small and both female and male gonophores
P. SCHUCHERT
728
FIG. 27
Eudendrium arbuscula Wright, 1859, male blastostyles in preserved material from Northern
Ireland.

developed on normal hydranths and not reduced blastostyles. Hamond's material most
probably belongs to an unnamed species. It could not be named here as Hamond’s
description is not complete enough and no material could be located. Note that also the
fertility period given by Hamond (summer) does not agree with the observations of
Faasse & Vervoort (2005) made for E. arbuscula of the neighbouring Dutch coast.
Eudendrium calceolatum Motz-Kossowska, 1905 Fig. 28
Eudendrium calceolatum Motz-Kossowska, 1905: 59, fig. 2. – Picard, 1955: 182. –
Marinopoulos, 1992: 58, figs 1.7, 2.1. – Marques et al., 2000b: 203.
DIAGNOSIS: Sparingly branched colonies, hydranth with belt of large nema -
tocysts, some capsules also dispersed. Gonophores on normal hydranth, male one two-
chambered, female ones with spadix that has a distal triangular swelling (axe-like
shape). Complementary capsules are large microbasic euryteles (Marinopoulos, 1992),
(20-30)x(8-13)μm, on hypostome, body, and hydrocaulus; shaft in undischarged
capsule thick, with two swellings, spanning 2/3 of capsule.
DESCRIPTION: See Motz-Kossowska (1905).
DISTRIBUTION: Endemic to the Mediterranean, recorded from Banyuls (Motz-
Kossowska, 1905), Algeria (Picard, 1955), and Marseille (Marinopoulos, 1992). Type
locality: Banyuls-sur-Mer, close to marine laboratory, on Cystoseira algae of rocky
littoral.
REMARKS: This is an insufficiently known species and Marques et al. (2000b)
considered it dubious. Marinopoulos (1992; via pers. com. by J. Picard) mentions that
is now very rare, although it was once common in the vicinity of Marseille. The spe-
cies is characterized by the axe-shaped spadix of the female gonophore.
Eudendrium capillaroides new spec. Figs 29-30
? Eudendrium teissieri. – Fey, 1970: 392. [nomen nudum]
? Eudendrium tessieri. – Castric et al., 1987: 97, fig. [note variant spelling]
TYPE MATERIAL: Syntype colonies MHNG INVE36293; Atlantic Ocean, France,
Britanny, Bay of Morlaix, more than 20m depth, 13 Sept. 2004, female colonies on ascidians
(including also Styela clava), accession number of partial 16S gene sequence AM991306.
OTHER MATERIAL: France, Camaret near Brest, depth 20-30m, 18 Sept. 2006, infertile co-
lony on Nemertesia antennina, not preserved, used to make DNA, 16S sequence identical to
AM991306.
DIAGNOSIS: Colonies small, monosiphonic, female gonophores borne on
incompletely developed hydranths, these later reduced entirely or nearly so, spadix
simple; males unknown; cnidome comprises two euryteles of slightly different size
(length ratio 1.3).
DESCRIPTION: Colonies small, monosiphonic, sparsely and irregularly branched,
up to 10 hydranths per stem. Perisarc smooth with occasional short annulated or irre-
gularly corrugated stretches, usually at origin of branches and hydranth pedicels.
Hydranths with up to 25 tentacles, hypostome relatively large, tentacular nematocyst
confined to proximal 2/3 of tentacles, arranged in regular rings, nematocyst oblique to
tentacle axis giving it thus a spiny appearance. Perisarc groove on hydranth body well
marked, relatively distal (basal third of body, Fig. 29B).
729
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4

Female gonophores (up to 6) formed on blastostyles that concomitantly develop
about 12-18 tentacles of reduced size, tentacles later atrophied, no hypostome formed,
spadix simple, long and thin (Fig. 29D). In older stages tentacles strongly atrophied or
lost, spadices shed and the embryos in their transparent capsules attached irregularly
along the pedicel of the former blastostyle (Fig. 29E-F).
Male gonophores not known.
Nematocysts: microbasic euryteles of two different size classes (Fig. 30), size
ratio of length of larger and smaller eurytele 1.3, ratio of width of larger and smaller
eurytele 1.4, larger capsule thus somewhat thicker. Smaller capsule abundant on tenta-
cles, also on hydranth body and coenosarc. Larger capsules (complementary nemato-
cysts) scattered in a band above the perisarc grove and also in coenosarc of stem and
pedicels.
DIMENSIONS: Stems 5-12 mm high; hydranth height about 0.3-0.4 mm, width
0.2-0.35 mm; hydranth pedicels diameter 0.12 mm, stem diameter at base 0.12-0.13
mm; encapsulated eggs about 0.2 mm. Nematocyst dimensions in preserved material
see table 1.
P. SCHUCHERT
730
FIG.28
Eudendrium calceolatum Motz-Kossowska, 1905, infertile and fertile hydranth, note particular
shape of spadices, scale bar 0.5 mm, modified from Motz-Kossowska (1905).
TABLE 1. Eudendrium capillaroides new. spec., dimensions in [μm] and proportions of nemato-
cysts, values from two preserved colonies
length of width of length of width of
tentacular tentacular larger larger
capsules capsules capsules capsules
mean 6.5 2.7 8.5 3.9
s. error of men 0.30 0.34 0.27 0.18
range 6-7.5 2.5-3.5 7-9 3.5-4.5
number of values 25 25 24 24
ratio 2.4 2.2
length/width

731
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 29
Eudendrium capillaroides new spec., after preserved type material. (A) One stem of colony,
scale bar 1 mm. (B) Hydranth, scale bar 0.1 mm. (C) Early developmental stage of female blasto -
style, scale bar 0.1 mm. (D-F) Later stages of female blastostyle, note atrophy of hydranth and
tentacles, same scale as C. (G) Cnidome: two microbasic euryteles of different size classes, pairs
of intact and discharged capsules, scale bar 10 μm,

BIOLOGY: Occurs in depths of 20-30 m.
DISTRIBUTION: Brittany. Type locality: France, English Channel, Bay of
Morlaix, about 20 m depth.
ETYMOLOGY: The specific epithet refers to the similarity to E. capillare, a
species with which it was initially confused.
REMARKS: This species resembles very closely E. capillare, the only difference
being their cnidomes. The cnidome of E. capillaroides comprises heteronemes of two
slightly different size classes, the ratio of their lengths being 1.3. The larger capsule is
somewhat thicker, the width ratio of the two types being 1.4. Although the dimensions
intergrade somewhat (table 1, Fig. 30), it is rather easy to see in a microscopic squash
preparation that there are actually two different populations of capsules. The cnidome
makes it immediately distinguishable from the otherwise similar E. merulum which has
much larger complimentary euryteles (see key to species). 16S sequence data
confirmed that E. capillare, E. capillaroides, and the European E. merulum are clearly
distinct lineages (Fig. 2). A species with a similar cnidome is E. maorianus Schuchert,
1996 from New Zealand, whose morphology, except for the bifid spadix, is almost
identical. Also E. maorianus has two types of euryteles that differ only minimally, the
ratio being also about 1.3. Interestingly, its 16S sequence is also rather similar to E. ca-
pillaroides (Fig. 2).
P. SCHUCHERT
732
FIG. 30
Eudendrium capillaroides new spec., frequency distribution of the lengths of the two nema tocyst
capsules, length in μm.

It is likely that E. capillaroides corresponds to the invalid nominal species
Eudendrium teissieri. Fey (1970), in a study dealing with the hydroids of the Glenan
Islands in southern Brittany, listed also Eudendrium sp. 3, with a remark that this spe-
cies would be described as E. teissieri by Cabioch in a forthcoming publication.
However, this apparently never happened and the name Eudendrium teissieri is not
valid (ICZN art. 13.1). It was not possible to locate any original material. Castric &
Michel (1982) and Castric et al. (1987) later included the name in a key to a faunistic
guide under the name Eudendrium tessieri [note different spelling], solely providing a
sketch of the hydranth and the complementary nematocysts. Also this publication
cannot be seen as a valid introduction of the name. There is no accompanying text, but
the sketch indicates that the complementary nematocysts are relatively small and
concentrated in a band on the hydranth body.
Eudendrium vaginatum Allman, 1863 Figs 31-32
Eudendrium vaginatum Allman, 1863: 10. – Allman, 1872: 339, pl. 14 figs 7-8. – Jäderholm,
1909: 53, pl. 3 figs 10-11. – Nutting, 1901: 167, pl. 15 figs. 3-6. – Fraser, 1944: 76, pl.
13 fig. 52.
not Eudendrium vaginatum. – Bonnevie, 1898a: 484, pl. 26 figs 24-26. – Weill, 1934a: 77, text-
fig. 70a-b. – Weill, 1934b: 389, text-fig. 239.
? Eudendrium vaginatum– Berrill, 1952: 22, figs 7-8.
Eudendrium annulatum. – Levinsen, 1893: 154. – Schuchert, 2001: 26, fig. 15A-C. [not
Eudendrium annulatum Norman, 1864]
in part Eudendrium vaginatum. – Marques et al. 2000a: 107, fig. 85. [others = E. annulatum]
MATERIAL EXAMINED: BMNH 1912.12.21.99; Scotland, Shetland Islands, Balta Sound;
depth 90m, non-type specimen; coll. A. M. Norman (material of Norman, 1869), all soft tissues
gone, colony typical. – ZSM 20040386, as Eudendrium insigne; Norway, Bergen; no collection
date; infertile colonies on laminarian algae, with numerous well preserved hydranths, undis-
charged larger microbasic euryteles with shaft coiled near origin. – RMNH Coel28403; as
Eudendrium insigne; Norway, Bergen; slide made of ZSM 20040386. – RMNH Coel28437;
65.42°N 52.93°W; Greenland, Sukkertoppen; slide preparation; female, but tissues damaged,
depicted in Marques et al. 2000a, has large microbasic euryteles, undischarged shaft curved near
origin. – IRSNB IG11365; Canada, Newfoundland, Trinity Bay, whaling station; material men-
tioned of Leloup (1939b); well preserved male colony, has typical large eurytele with coiled
shaft. – Norway, Korsfjord, Great Skorpa Island; depth 80-160m; triangular dredge; 16 June
2006; on rock; infertile, material not preserved. – Icelandic Museum of natural History, sample
BIOICE2000; 65.354°N 13.794°W; Iceland; 26m; 18 July 1987; infertile; figure published in
Schuchert (2001) as E. annulatum; re-examined material & changed id. 4 Apr. 2007.
DIAGNOSIS: Branched colonies, mostly polysiphonic when mature, straggling
growth, perisarc often dark-brown, rigid, sharply and regularly annulated throughout,
with bark (stolonal overgrowth of stem), irregular, convoluted; perisarc originates in
groove in upper half of hydranth body and not at base, in preserved material giving
impression of pseudohydrotheca; complementary capsule a microbasic eurytele with
one small coil in undischarged capsule, discharged shaft longer than capsule.
DESCRIPTION: Colonies much branched, shrubby, straggling in appearance,
rather stiff and bristly, stem thick, monosiphonic or more usually polysiphonic,
branches mostly monosiphonic and short, branching irregular, branches often curved
and of uneven length. Hydrorhiza creeping stolons, anastomosed to tight-meshed net
on even surfaces, smooth perisarc. Tubes of stem and branches comparatively thick,
733
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4

P. SCHUCHERT
734
FIG. 31
Eudendrium vaginatum, all except of E after preserved material, D redrawn from Jäderholm
(1909). (A) Colony silhouettes, top colony from Iceland, below one from the Shetland Islands,
scale bar 5 mm. (B) Hydranth with the characteristic pseudohydrotheca, scale bar 0.2 mm. (C)
Part of branch showing the annulation of the perisarc that is present throughout the colony, scale
bar 0.2 mm. (D) Young male gonozooid, in more advanced stages the hydranth is reduced
variably, scale bar 0.5 mm. (E) Nematocysts: small undischarged microbasic eurytele, large
undischarged and discharged microbasic euryteles; scale bar 10 μm.

annulated throughout, annulation distinct and very regular (Fig. 31C). Base of colony
often overgrown by smooth, contorted, stolon-like tubules forming a bark-like
covering.
735
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 32
Eudendrium vaginatum Allman, 1863, native capsules from Norwegian material, scale bar 10
μm. (A-D) Undischarged capsule, the four sections depict the same capsule, but in different
focusing planes, note the small coil of the shaft near its origin. (E) Discharged capsule, note the
length of shaft which surpasses the capsule length.

Hydranths with 18-20 tentacles, perisarc originates as thin film in well defined
groove in upper half of fully grown hydranth body, perisarc thus forming a charac -
teristic closely adhering cup-like pseudohydrotheca (or loose and collar-like in
preserved material that has undergone some tissue shrinking).
Gonophores on normal or somewhat atrophied hydranths. Male gonophores
initially on normal hydranths, in more advanced stages reduced (hypostome
disappears, tentacles shorten, body gets smaller), gonophores two chambered, more
than 10 per hydranth. Female gonophores with unbranched spadix on normal polyps or
polyps with shortened tentacles, hypostome present (at least in younger stages), six or
more gonophores per hydranth.
Colours: perisarc light to dark brown, sometimes almost black; soft tissues cha-
racteristically red.
Nematocysts: small tentacular microbasic euryteles and large microbasic eury-
teles, in dense ring on hydranth body primarily along groove and on hypostome, shaft
in undischarged capsule thick, forming a small, complete coil near junction to capsule
wall (Figs 31E, 32A-D), coil diameter about 1/10 of capsule length; discharged shaft
distinctly longer than capsule (s>1.5, Fig. 32E), thick, distal half much swollen, barbed
even along narrow part, tread thick.
DIMENSIONS: Colonies up to about 3 cm high. Hydranth height from base to
mouth about 0.5 mm. Hydranth pedicel diameters 0.2-0.4 mm. Annulation of perisarc
50-70 μm high. Small microbasic euryteles (7-8)x(3-4), r=2-2.8; large microbasic
eurytele (20-23)x(9-9.5) μm, r= 2.2-2.6.
BIOLOGY: Depth range 0-180 m, known substrates are rock and laminarians.
DISTRIBUTION: An Arctic to northern boreal species, with reliable records from
the Shetland Islands (Allman, 1864; this study), Norway (this study), Jan Mayen
(Jäderholm, 1909), Iceland (Schuchert, 2001 as E. annulatum; this study), Western
Greenland (this study), Newfoundland (Leloup, 1939; this study). Pacific records (e. g.
Nutting, 1901; Stechow, 1913; Fraser, 1937) need confirmation by examining their
nematocysts. Type locality: Shetland Isles, in rockpools at ELS level and below.
REMARKS: Eudendrium vaginatum Allman, 1863 is a characteristic species that
can also be identified in the absence of gonophores. The hydranth produces the perisarc
from a circular groove located in the upper half of the hydranth body, this in contrast
to most other Eudendrium species where it is located in the basal region. The newly
formed filmy perisarc thus adheres to the lower part of the hydranth like a pseudo-
hydrotheca (easier to observe in preserved material that has undergone some tissue
shrinking). Further characteristic traits of the species are the completely and regularly
annulated perisarc, the dark-brown colour of the perisarc, and the red colour of the
living tissues. Although the high position of the groove is very typical for this species,
the location could be variable to some degree, but in the examined hydranths (>30), the
vast majority had the groove in the upper half of the hydranth.
Although the type material could not be examined – it could not be found in the
museums of London, Edinburgh nor Dublin – the characteristics listed above allow to
identify the samples listed above quite unambiguously as belonging to Allman's
Eudendrium vaginatum. Several of these samples permitted the examination of the
P. SCHUCHERT
736

nematocysts. Besides the normal tentacular microbasic euryteles, there is also a large
microbasic eurytele with a relatively long and thick shaft. The discharged shaft is
distinctly longer than the capsule, but the ratio is smaller than 2.5, which qualifies it as
a microbasic eurytele. In the undischarged capsule, the shaft forms a characteristic tiny
coil near the junction with the capsule wall (Figs 31E, 32). This type of capsule is
rather uncommon, but another Eudendrium in the NE Atlantic has a similar, but
distinguishable capsule (see Eudendrium unispirum; coil in capsule ca. 1/3 of capsule
length).
With these results at hand, it is thus evident that E. vaginatumAllman, 1863 and
E. annulatum Norman, 1864 are distinct species. Both species have occasionally been
synonymized (e. g. Marques et al., 2000a). When Normann (1864) described E. annu-
latum, he stated: "the tubes [hydranth pedicels] are not expanded at their extremities to
receive the polypites, as is the case in some allied species". This remark certainly
concerns E. vaginatum, which at the time of Norman's writing (December 1863) had
already been published (January issue of the same journal). This is also reflected in his
Latin diagnosis: "... polypis calices non expansos obsidentibus,..." Thus Norman like-
ly wanted to keep his species distinct from Allman's one. Although I found some
Eudendrium annulatum hydranths with a filmy perisarc collar (Fig. 21C), these were
rare and rather small, unlike in typical E. vaginatum where they extend up to the
middle of the body of fully grown hydranths (Fig. 31B). The perisarc of Eudendrium
annulatum, despite its name, is not annulated throughout. Both E. annulatum and E.
vaginatum form a bark-like covering of the stem base. In the former species (Fig. 23)
it is rather regular and sheet-like, while in the latter it is more irregular and convolu-
ted. Moreover, Norman has also found Eudendrium vaginatum at Shetland and he kept
it distinct from his E. annulatum (see Norman, 1869). Norman's specimen (BMNH
1912.12.21.99) was re-examined for this study and it is evidently E. vaginatum (the
nematocysts could not be examined, though).
Although Jäderholm's (1909) material could not be re-examined, his figures of
the hydranth and the perisarc leave no doubt that his identification as E. vaginatum
must be correct.
The material from Iceland described in Schuchert (2001) as E. annulatum was
re-examined for this study. It is clearly referable to E. vaginatum and not E. annu latum.
Nutting (1901) attributed some samples from Alaska to Eudendrium vaginatum.
Although his material was also completely annulated and possessed pseudohydro -
thecae, I think it could belong to a separate species as the female gonophores were
borne on reduced hydranths. An examination of the nematocysts is necessary to
establish the identity of the Alaskan population.
A number of other authors thought to have found Eudendrium vaginatum.
However, as it has been confounded regularly with E. annulatum or E. insigne, most
records are likely incorrect.
Eudendrium unispirum new spec. Fig. 33
TYPE MATERIAL: Syntypes, BMNH 1948.9.8.82; several stems of one colony, originally
identified as Eudendrium album; England, Plymouth; collected 1898 by E. T. Browne; growing
on Tubularia indivisa; male colony.
737
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4

OTHER MATERIAL: BELUM Md621; Northern Ireland, Down, Strangford Lough, W of
Colin Rock, 54°25.54' N 005°36.33' W, depth 24m, 7 June 1989; infertile colony. – BELUM
Md622; Northern Ireland, Down, Strangford Lough, SE of Abbey Rock, 54°25.51'N
05°35.12'W, 15m depth, 1 June 1983: infertile colony on stem of T. indivisa. – Spitzbergen,
Svalbard, Hornsund, 2 small infertile colonies, coll. 12. July 2000 and 18 July 2006, depth about
16m, in private collection of Marta Ronowicz.
DIAGNOSIS: Small branched monosiphonic colonies, complementary nema -
tocysts microbasic eurytele with shaft 2-2.4 times as long as capsule, in intact capsule
coiled 1-1.5 times, coil large (> 1/3 capsule length). Male sporosacs on intact
hydranths.
DESCRIPTION: Colonies delicate, bushy, monosiphonic, larger colonies much
branched with up to 40 hydranths per colony, branching irregular, branches long.
Perisarc mostly smooth, some annulation present, annulation usually present at origin
of new branches and hydranth pedicels. Hydranths typical for genus but relatively
small, 20-30 tentacles (mostly 24), on body a few scattered large nematocysts, more in
circle around mouth, perisarc groove near base of body, usually difficult to see.
Developing hydranth buds with layer of contiguous large euryteles.
Male sporosacs develop on intact hydranths, 2-4 per hydranth, 1-2 chambered,
younger ones with distal tubercle with large nematocysts. Females unknown.
Nematocysts: small (tentacular) microbasic euryteles, shaft in intact capsule
thick; large microbasic euryteles, discharged shaft 2-2.4 times as long as capsule, with
spines along whole length but getting shorter towards capsule, in intact capsule shaft
coiled with one to 1.5 turns, usually in upper half of capsule, size and form of coil
somewhat variable from capsule to capsule but size > 1/3 capsule length, coiled part of
shaft thin.
DIMENSIONS: Colonies from a few mm to 20 mm high. Hydranth diameter 0.1-
0.18 mm, height from base to mouth 0.25-0.35 mm, hydranth pedicel diameter 0.06-
0.10 mm, diameter of stem near base 0.13-0.17 mm. Nematocysts (from 4 preserved
colonies): small microbasic eurytele (tentacular) (6.5-7.5)x(2.5-3.5)μm; large eurytele
(19-22)x(8-9.5)μm.
ETYMOLOGY: The specific epithet is derived from the Latin words uni (single)
and spirum (coil), an allusion to the conspicuous, single coil of the shaft in the
complementary eurytele capsule.
BIOLOGY: The known depth range is 15-24 m. Two colonies were found
growing on stems of Tubularia indivisa.
DISTRIBUTION: Plymouth (U. K.), Northern Ireland, Spitzbergen. Type locality:
Plymouth, on stems of Tubularia indivisa.
REMARKS: This species resembles closely E. album. In fact, except for the
complementary capsules, both species are identical. The undischarged complementary
capsules of E. unispirum present a shaft that has only 1-1.5 coils, this in contrast to E.
album which has four or five coils (Figs 6 and 33C). Also the lengths of the discharged
shafts are significantly different. In E. unispirum the ratio of shaft/capsule length (=s)
is 2-2.4, in E. album it is larger than 5. As these characters shows rather little variation
in E. album, the capsule of E. unispirum is quite reliably distinguishable. Applying
P. SCHUCHERT
738

currently used diagnoses (e. g. Bouillon et al., 2006), the shaft/capsule length ratio of
<2.5 qualifies the complimentary capsules of E. unispirum as microbasic, while the one
of E. album is macrobasic. A similar eurytele with one coil in the undischarged capsule
is found in E.vaginatum (Fig. 32). However here the coil is very small and the species
is otherwise rather easily separable from E. unispirum (see key on page 684).
Colonies of Eudendrium unispirum and E. album were found to occur sympa-
trically (Plymouth and Strangford Lough), which can be regarded as another argument
for them being distinct species.
No female sporosacs could be found, but as the male sporosacs develop on nor-
mal hydranths, the same can also be expected for the female ones.
739
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 33
Eudendrium unispirum new spec., after preserved material, A and D from Northern Ireland,
B-C type material (A) Colony silhouette, scale bar 1 cm. (B) Hydranth with male sporosacs,
scale bar 0.1 mm. (C) Undischarged nematocysts: small and large microbasic eurytele, scale bar
10 μm. (D) Schema of discharged large microbasic eurytele, scale bar 10 μm.

Eudendrium capillare Alder, 1856 Fig. 34
Eudendrium capillare Alder, 1856: 355, pl. 12 figs 9-12. – Allman, 1864: 362. – Hincks, 1868:
84, pl. 14 fig. 2. – Allman, 1872: 335, pl. 14 figs 1-3. – Weismann, 1883: 109, pls 1-2. –
Jäderholm, 1909: 53, pl. 3 figs. 8-9. – Bedot, 1914: 79. – Vervoort, 1946: 154, fig. 62. –
Naumov, 1969: 263, fig. 132. – Calder, 1972: 226, pl. 2 fig. 6. – Millard & Bouillon,
1974: 17, fig. 3E-H. – Millard, 1975: 82, fig. 27E-J. – Kubota, 1976: 235, figs 3.7-8. –
Cornelius & Garfath, 1980: 278, type material. – Calder, 1988: 41, fig. 30-32, syno nymy.
– Hirohito, 1988: 77, figs 24g-h, 25. – Marinopoulos, 1992: 60, fig. 3.1. – Marques et al.,
2000a: 88, figs 28-34. – Marques et al., 2000b: 201. – Schuchert, 2001: 27, fig. 16A-F.
– Peña Cantero & García Carrascosa, 2002: 27, fig. 4a-b. – Puce et al., 2005: 202, figs
1b & 2c.
Corymbogonium capillare. – Allman, 1861: 171.
? Eudendrium humile var. corymbifera Allman, 1863: 10.
Eudendrium tenellum Allman, 1877: 8, pl. 4 figs 3-4. – Kramp, 1914: 99. – Fraser, 1937: 43, pl.
8 fig. 3. – Yamada, 1954: 17, fig. 15. – Calder, 1972: 226, pl. 2 fig. 8. – Hirohito, 1988:
88, fig. 31d-h. – Schuchert, 2001: 33.
Eudendrium hyalinum Bonnevie, 1898b: 7. – Bonnevie, 1899: 50. – Naumov, 1969: 263,
synonym.
Eudendrium tenue A. Agassiz, 1865: 160, fig. 250. – Bedot, 1914: 79, synonym.
Eudendrium parvum Warren, 1908: 272, fig. 1, pl. 45 figs 1-4. – Millard, 1975: 82, synonym
? Eudendrium capillare var. mediterranea Neppi, 1917: 30, fig. 1, pl. 4 figs. 1, 1a.
Eudendrium sagaminum Yamada, 1954: 14, fig. 12. – Hirohito, 1988: 77, synonym.
not Eudendrium capillare. – Kramp, 1932a: 18. – Kramp 1932b: 7. [= E. album]
? not Eudendrium capillare. – Ramil & Vervoort, 1992: 18, fig. 1b-c.
TYPE MATERIAL EXAMINED: Syntype material of E. hyalinum, Bergen Museum no. 13628;
Skjærgården St. 5-6, and no 10854, Bergens Skj. St. 3, 4, 5; 30-35 m. Both colonies infertile, ori-
ginating from the vicinity of Bergen.
OTHER MATERIAL EXAMINED: MHNG INVE29390 Atlantic, France, Brittany, near St. Pol
de Léon, 6 June 2000; depth 20m; on Ciona intestinalis; female colony; no haplonemes found;
16S sequence, AY787884. – Mediterranean, France, Banyuls-sur-Mer, October 1991, female
colony on Phallusia mammilata, not preserved. – MHNG INVE32951; Mediterranean, France,
port of Banyuls-sur-Mer; 9 May 2002; haplonemes present; depth 1m; male; 16S sequence
AM991296. – MHNG INVE34231; Italy, Naples, Nisida; 14 April 1911; depth 1m, female. –
MHNG INVE34234; Italy, Naples, Santa Lucia; 14 April 1911; depth 1m; male. – MHNG
INVE36196; Mediterranean, France, Bay of Marseille; 24 April 1970, depth 5m; male and
female colonies. – ZSM, Stechow collection; England, Plymouth, female. – BELUM Md616;
Scotland, Outer Hebrides, St. Kilda, Levenish; 57.792°N 08.509°W; depth 30m; 18.07.1982;
males and females. – BELUM Md619; Northern Ireland, Strangford Lough Narrows, Cloghy
Rocks; 54.355°N 05.546°W; 7.5 m; 04.08.1983; males. – BELUM Md620; Northern Ireland,
Strangford Lough Narrows, Rue Point; 54.365°N 05.541°W; depth 6m; 11.08.1983; females. –
MHNG INVE37298; Atlantic, France, Normandy, Herquemoulin, Treize Vents; 22 Aug 2005;
0m; male; haplonemes rare; 16S sequence AM991295. – MHNG INVE54569; England;
Plymouth, Firestone Bay; depth 12-18 m; 19 June 2007; on sponge and Tubularia; fertile fema-
le colony; haplonemes present; 16S DNA sequence AM991294. – MHNG INVE54592;
England; Plymouth; depth 25m; 26 June 2007; on Tubularia indivisa; fertile female colony;
haplonemes present. – England; Plymouth, Mew Stone; depth 25m; 23 June 2007; infertile
colony; haplonemes present; material not preserved. – MHNG INVE54602; Spain; Basque
Countrty, Guipúzcoa, Fuenterrabía; 0m depth; 12 July 2007; floating docks of harbour; fertile
female colony; haplonemes present; 16S DNA sequence identical to AM991294. – MHNG
INVE54696; Northern Ireland; Strangford Loch; 26 July 2007; fertile male colony; haplonemes
present; 16S DNA sequence identical to AM991294.
DIAGNOSIS: Small monosiphonic colonies, cnidome comprises small microbasic
euryteles and facultatively isorhizas of about the same size, both not concentrated in
basal ring. Male blastostyle without tentacles, females with or without short tentacles,
later atrophied, spadix simple.
P. SCHUCHERT
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741
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 34
Eudendrium capillare Alder, 1856; after preserved Mediterranean (B, D, H, I) and Atlantic
(A, C, E-G, J) material. (A) Colony silhouette, scale bar 1 cm. (B) Single stem, scale bar 2 mm.
(C) Higher magnification of branch with smooth and annulated perisarc, scale bar 0.1 mm. (D)
Male blastostyle, scale bar 0.2 mm. (E-H) Sequence of development of female blastostyle, note
the presence of short tentacles. In later stages (H) the blastostyle is completely reduced, scale bar
0.2 mm. (I) Encapsulated embryos attached to the former blastostyle pedicel, same scale as E.
(J) Nematocysts: intact and discharged microbasic euryteles; intact and discharged haplonemes;
scale bar 10 μm.

DESCRIPTION: Colonies small, delicate, monosiphonic, usually irregularly
branched. Perisarc smooth with occasional short annulated or irregularly corrugated
stretches, usually at origin of branches and hydranth pedicels. Hydranths with about 20
tentacles (15-24 range), hypostome relatively large, tentacular nematocyst confined to
proximal 3/4of tentacles, arranged in regular rings, nematocyst oriented obliquely to
tentacle axis, giving it thus a spiny appearance.
Male gonophores borne like tuft on blastostyles without tentacles at all stages,
12-15 gonophores and more per blastostyle, one- to three chambered, sometimes with
terminal tubercle without nematocysts.
Female gonophores borne on hydranths with much shortened tentacles and
body much reduced, hypostome absent; 5-12 eggs per blastostyle, with curved and
unbranched spadix; in older stages tentacles completely atrophied. After fertilization
the spadices are shed and the embryos in their transparent capsules attached irregu larly
along the pedicel of the former blastostyle.
Nematocysts: microbasic euryteles, one end tapering, not concentrated in a
basal ring; isorhiza capsules with two blunt ends, same size as euryteles, numbers
present rather variable, may be missing.
Colours: variable, either not much coloured, cream to light rose-orange, or red.
DIMENSIONS: Colony heights when mature 5 mm to 4 cm; hydranths 0.3-0.43
mm high (incl. hypostome), diameter of body 0.2-0.34 mm; stem diameter at base
0.12 mm; length of male gonophores 0.3-0.35 mm; embryos in capsules 0.2 mm.
Microbasic euryteles (preserved material): Atlantic (3 colonies) (6-8)x(2.5-3) μm, r=
2.3-2.8; Mediterranean (3 colonies) (5.5-9)x(2.5-4)mm, r=2.4-2.9. More measure-
ments for other regions are given in Millard & Bouillon (1974), Millard (1975), Kubota
(1976), Calder (1988), Marques et al. (2000b), and Peña Cantero & García Carrascosa
(2002). All lie more or less within the limits given above. Haplonemes (preserved ma-
terial): (5-6) x(2-2.5)μm.
OTHER DATA: Weismann (1883) described the oogenesis and the development of
the female gonozooids. The oogonia become first visible in the gastrodermis of the
coenosarc, although he could not localize their origin. The oogonia are present before
the gonozooids develops. Fertilization takes place while the eggs were still clasped by
the spadix. Later the spadix is shed and the embryos develop a chitinous envelope
(similar to E. racemosum, see Fig. 9E). Neppi (1917) described the metamorphosis of
the planula.
BIOLOGY: Occurs usually from zero to about 80 m depth, deeper records are
known. Mature colonies have been observed May to September (NE Atlantic) or April
to November (Mediterranean). The reproductive period is likely longer than indicated
by these intervals. Grows on a variety of solid substrata and other animals and algae.
Boero & Fresi (1986) found it regularly, sometimes abundantly, in a rocky zone of the
Mediterranean. See also Boero (1981).
DISTRIBUTION: Reportedly nearly cosmopolitan, but only identifications using
nema tocyst information are reliable. Reliable records are from the northeastern
Atlantic, Greenland, the Mediterranean, Bermudas, southern Africa, and Japan
(Millard & Bouillon, 1974; Millard, 1975; Kubota, 1976; Calder, 1988; Schuchert,
P. SCHUCHERT
742

2001). Along the European coasts certainly occurring from Norway to Gibraltar,
including the North Sea but not the Baltic Sea (Jäderholm, 1909; Bouillon et al., 1995;
Peña Cantero & García Carrascosa, 2002; this study), also frequent in the
Mediterranean (Marques et al., 2000a, 2000b). Type locality: North Sea, Embleton
Bay, Northumberland, Great Britain, on the hydroid Nemertesia ramosa.
REMARKS: Contrary to most other authors (Millard, 1975, South Africa; Watson,
1985, Australia; Calder, 1988, Bermuda; Marques et al., 2000a Mediterranean), I
occasionally found two types of nematocysts in this species. Besides the abundant,
almond-shaped microbasic eurytele, there is a differently shaped haploneme (isorhiza,
see Fig. 34J). It occurred in much lower and rather variable numbers. In some samples
it was absent or very rare (Mediterranean), in others it was rare to quite frequent (NE
Atlantic). Also Marinopoulos (1982) observed isorhizas in this species, although his
schematic drawing (fig. 1.3) shows a different shape. The colonies which had them in
higher numbers (Atlantic specimens) were indistinguishable from others in which
these capsules were not noted. Because these capsules are usually much less frequent
and have approximately the same size as the euryteles, they are very easily overlooked.
Moreover, they discharge rarely in microscopic preparations. Preliminary 16S
sequence data (Fig. 2) of colonies with haplonemes (see Material examined) and one
colony in which it could not be found (MHNG INVE29390, AY787884) clustered all
in one clade. I therefore assume that they all belong to one species and that E. ca pillare
has variably also small haploneme capsules.
I have examined the type material of E. hyalinum Bonnevie, 1898b. The
colonies are small, sparingly branched and infertile. I found only small capsules of one
size class. Eudendrium hyalinum Bonnevie, 1898b is thus here regarded as a synonym
of E. capillare as has been done before by Naumov (1969).
Allman (1877) described E. tenellum from infertile material without hydranths,
he was even not sure whether it was a Eudendrium. This species – although it has been
repeatedly identified by other authors – must certainly be considered unrecognizable.
It was thought to be conspecific with E. capillare by Naumov (1969), but other authors
like Calder (1972) kept it distinct from E. capillare on account of its non-reduced male
gonozooids. I have seen type material of this species. There are only few fragments left
containing only little soft tissue. There is apparently only one type of nematocyst
present like in E. capillare and E. tenellum may be regarded as synonym of E. capilla-
re (see also Bulletin of Zoological nomenclature Volume 64(3), opinion 2175; on type
specimen).
Working with colonies from the Gulf of Naples, Weismann (1883) and Neppi
(1917) observed that their colonies had female gonozooids with some tentacles, which
were nevertheless reduced in later stages. The male sporosacs had terminal nematocyst
tubercules (Neppi, 1921). This prompted to Neppi (1917) to propose a variant name for
this population, namely Eudendrium capillare var. mediterranea. As such a tentacle
formation of the female gonozooid has also been observed in other populations (e. g.
Millard, 1975; Calder, 1988; Schuchert, 2001; this study), Neppi's variant is likely not
distinct from the nominal form, although the absence of information on the nema -
tocysts precludes any reliable conclusion. Marques et al. (2000b) think that Neppi's
variant does not belong to E. capillare, but the lack of information precludes a reliable
identification.
743
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4

Material from Greenland described in Schuchert (2001) had much less reduced
female and male blastostyles. The same morphotype, or sometimes with even less
reduced blastostyles, was also found at Spitsbergen (M. Ronowicz, pers. com.; MHNG
INVE60719). The slight morphological differences in observed in these Arctic
populations could be either due to population or environmental differences, or more
likely an indicator of two separate species being involved. Genetic data from these
populations are needed for a further assessment.
Eudendrium armatum Tichomiroff, 1887 Fig. 35
Eudendrium armatum Tichomiroff, 1887: 31, fig. 25, pl. 1 figs 3-4, pl. 2, figs 3-4. – Wasserthal,
1973: 93, figs 1-40. – Laukötter, 1985: 67, figs 1-15. – Boero & Fresi, 1986: 141. –
Marinopoulos, 1992: 60, fig. 1.4. – Marques et al., 2000a: 82, figs 16-18. – Marques et
al., 2000b: 202. – Puce et al., 2005:202, figs 1a, 2a, 2e.
not Eudendrium armatum Jäderholm, 1907: 372. – Jäderholm, 1909: 52, pl 4 figs 7-9. [ = Euden -
drium cnidoferum Stechow, 1919]
MATERIAL EXAMINED: MHNG INVE39474; France, Marseille, Riou-Impériaux de Terre;
depth 37m; 9 July 1966; male and female colonies. – MHNG INVE29458; Greece, Island of
Paros; depth 1-2m; 1 Sept. 1990; infertile colony. – MHNG INVE4987; Italy, Naples; 23 Feb.
1892, infertile. – MHNG INVE49886; Italy, Naples; collected 1896, female.
DIAGNOSIS: Colonies polysiphonic, with long nematophores replacing
hydranths, male blastostyles fully developed hydranths, female blastostyles hydranths
with short tentacles. Only microbasic euryteles of one size class.
DESCRIPTION: Colonies much branched, polysiphonic, tree- or bush-like.
Hydranths typical for genus, basal groove near base, approximately 24 tentacles,
proximal portion of tentacles devoid of nematocysts, density gradually increasing
towards distal, in untidy bands, axis of capsules parallel to tentacle and thus tentacle
surface not spiny. Some hydranths replaced by long, filiform, contractile nemato -
phores, epidermis of nematophores studded densely with nematocysts, gastrodermis
parenchymatic.
Male sporosacs 2-3 chambered, no terminal nematocyst button, up to 14 carried
on fully developed hydranths, small minority with reduced tentacles.
Female gonophores with simple, curved spadix, up to 14 on hydranth with
hypostome, somewhat smaller than usual hydranth body and short, stubby tentacles.
Fertilized eggs get encapsulated and attached to pedicels of blastostyle.
Nematocysts: only one type and size of microbasic euryteles, discharged shaft
shorter than capsule.
DIMENSIONS: Fertile colonies 2-8 cm high, hydranths 0.5-0.6 mm high, diameter
of hydranth pedicels 0.11-0.13 mm, diameter of basal stem tubes ca. 0.18 mm.
Microbasic euryteles (6-7)x(3-3.5)μm, r=2.0-2.3.
BIOLOGY: Abundant in certain regions of the Mediterranean, from 1 to 40 m,
generally on rocks. Gonophores present February-March, July-October (Boero &
Fresi, 1986; Marques et al., 2000b).
Wasserthal (1973) described the egg, gonophore and blastostyle development in
great detail. Laukötter (1985) provided the same information for males.
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745
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 35
Eudendrium armatum Tichomiroff, 1887, after preserved Mediterranean material. (A) Colony
silhouettes illustrating variation of growth form and density, scale bar 1 cm. (B) Branch with
hydranth and contracted nematophore, scale bar 0.5 mm. (C) Nematocysts: undischarged micro-
basic eurytele, scale bar 10 μm. (D) Young, developing male blastostyle, scale bar 0.2 mm. (E)
Mature male blastostyle (intact hydranth), same scale as in D. (F) Young, developing female
blastostyle, same scale as D. (G) Female blastostyle (slightly reduced hydranth) with mature
eggs held by spadix; same scale as D. (H) Advanced mature female blastostyle and encapsu lated
embryos attached to pedicel, same scale as D.

DISTRIBUTION: Endemic to the Mediterranean, present in the western and eastern
Mediterranean (Marques et al., 2000b; this study). Type locality: Mediterranean.
REMARKS: Although its nematophores make it easily recognizable, Eudendrium
armatum has likely been repeatedly confused with the similar E. rameum.
Eudendrium vervoorti Marques & Migotto, 1998 Fig. 36
Eudendrium vervoorti Marques & Migotto, 1998: 149, fig. 1. – Faasse & Vervoort, 2005: 60,
figs 1-2.
DIAGNOSIS: Small monosiphonic colonies, female gonophores without spadix,
attached via long pedicels to normal hydranths, only small microbasic euryteles of one
size class.
DESCRIPTION: Colonies small, sparingly branched, monosiphonic. Perisarc
mostly smooth, some indistinct rings, no clear annulation. Hydranths rather slender, no
distinct basal groove, 15-20 tentacles. Female gonophores arising from body of normal
hydranths, 2-6 per hydranth, without spadix, tentacles and hypostome of blastostyle not
reduced during later development. Mature eggs (embryos?) encapsulated in thin
perisarc, linked by long peduncles to basal part of hydranth or to hydranth-pedicel,
distal part broadened. Male gonophores unknown. Nematocysts: microbasic euryteles
of one size class (5.3-5.8)x(3.3-3.6)μm, r= 1.6.
DIMENSIONS: Colonies up to 7 mm, hydranth ca. 0.57 mm high and 0.15 wide,
branches 0.13 mm in diameter, eggs 0.22-0.28 mm.
BIOLOGY: Found once in a shallow seawater pool separated from the sea.
DISTRIBUTION: Type locality only, 51.633°N 03.983°E, The Netherlands,
Zeeland.
REMARKS: This species is based on a single colony collected in 1962 and no
further records are known. The species is rather unique among the genus Eudendrium
as its female gonophores do not develop a spadix. In other Eudendrium species, a
spadix is always present, but often only during the initial stages of the gonophore
development. It could also be that the type material is an aberrant E. capillare and the
absence of a spadix due to some developmental abnormalities, e. g. caused by the
particular environmental conditions it was growing in. New findings must be obtained
to confirm the identity of the species.
PROBLEMATIC SPECIES
Myrionema multicornis (Allman, 1876) new comb.
Perigonimus multicornis Allman, 1876: 252, pl. 9 figs 1-2. – Kramp, 1926: 241.
Eudendrium ramosum. – Kramp, 1926: 241. [not Eudendrium ramosum (Linnaeus, 1758)]
TYPE MATERIAL EXAMINED – Syntype, BMNH 1877.4.12.21, as Perigonimus multicornis,
type, loc. Kattegatt, leg. G. Allman.
REMARKS: Allman (1876) based his description of Perigonimus multicornis on
samples sent to him by Christian Frederik Lütken of the Copenhagen Museum. The
specimens itself was collected by the botanist A. S. Ørsted. The provenience of the
P. SCHUCHERT
746

sample was purportedly from the Kattegat (Denmark). Allman identified it as a new
Perigonimus species characterized by the high number of tentacles (he gives 40 as
number).
Kramp (1926) re-examined the type material in possession of the Copenhagen
museum and recognized that it belonged to the Eudendriidae. He found that Allman
must have mistaken hydranth-buds for incipient gonophores. True female gonophores
were, however, present in the lower portion of the colony, arranged in a whorl on a
normally developed hydranth. The colony was monosiphonic and Kramp thus referred
it to Eudendrium ramosum. Kramp did not discuss the discrepancy of the tentacle
number, which is much too high for E. ramosum.
While working at the Natural History Museum in London, I found another
syntype specimen of Perigonimus multicornis (BMNH1877.4.12.21). It was given to
the museum by Allman in 1877 and is certainly a part of the original material he had
obtained from the museum in Copenhagen. An examination of these stems, growing on
an unidentifiable substrate (soft tube of a polychaete?), confirmed the description of
Allman, but more importantly also the observations of Kramp (1926). This specimen
evidently belongs to the Eudendriidae and it even has some fertile female hydranths.
The gonophores have a simple spadix and are arranged in a whorl at the base of a
normally developed hydranth. The hydranths are not well preserved, likely due to pre-
fixation damage by abrasion and compression, but it is evident that they are typical for
the Eudendriidae. However, the large numbers of tentacle is immediately striking and
they are arranged in two close-set whorls. I could find hydranths with up to 50
tentacles. An examination of the nematocysts showed that besides the usual small
microbasic euryteles there are also large macrobasic euryteles. The most revealing
feature, however, is the conspicuous presence of zooxanthellae in the gastrodermal
747
EUROPEAN ATHECATE HYDROIDS, FILIFERA 4
FIG. 36
Eudendrium vervoorti Marques & Migotto, 1998; modified after original publication, scale bar
0.5 mm. (A) Hydranth with putative developing eggs. (B) Hydranth with mature eggs.

layer. The zooxanthellae are especially well visible in the tentacles and some of them
still give a purple staining reaction with an iodine solution. By all means, this sample
is indistinguishable from Myrionema hargitti (Congdon, 1906) [e. g. MHNG
INVE60793 material from Guadeloupe or an unregistered sample from Belize]. The
other syntype colony is still in the museum of Copenhagen and it must also be attri -
buted to the genus Myrionema (Dr O. Tendal, ZMUC, pers. comm.). This makes it sure
that the syntype of the London museum was not confounded with another sample after
Allaman had deposited it.
Allman’s species is thus a senior synonym of Myrionema hargitti, a species that
is regarded by some authors as a synonym of the Pacific M. amboinense Pictet, 1893
(e. g. Calder, 1988). Mainly for biogeographic reasons I think that the Caribbean H.
hargitti should be kept distinct from the Pacific M. amboinense, but both species seem
also to differ in the tentacle numbers. Whatsoever, hydroids of the genus Myrionema
are confined to tropical regions and it is quite unlikely that the genus occurs along the
Danish coast. It is much more probable that the origin of the type material of M. mul-
ticornis was given incorrectly. The collector – Anders Sandøe Ørsted (1816-1872) –
was a well known Danish botanist who travelled and collected extensively in Central
America and the Caribbean (e. g. Ørsted, 1863). Allman obtained the sample from
Copenhagen certainly only after the death of Ørsted and it appears likely that some
labels were incorrect or were confounded before he obtained it.
Until the historic presence of Myrionema multicornis (Allman, 1876) in the
North Sea can be confirmed, it seems better to regard the type locality Kattegat of
Myrionema multicornis as doubtful. Because the type locality is doubtful, the name M.
multicornis should also not replace its junior synonym Myrionema hargitti (Congdon,
1906).
ACKNOWLEDGEMENTS
I wish to thank several colleagues who sent me loans or gifts of Eudendrium
samples: Drs Alvaro Altuna, Doris de Vito, Keith Hiscock, Plamen Mitov, Frédéric
Sinniger, Bernard Picton, and Stefania Puce. I also owe some special thanks to Dr. B.
Picton who invited me to examine the Eudendrium collection of the Belfast museum
and who provided a much appreciated accommodation. Dr. Maria Pia Miglietta kindly
sequenced some of the 16S gene fragments. I also profited very much from loans of the
natural history museums of Belfast, Bruxelles, Copenhagen, London, Leiden, Munich,
Oslo, and Stockholm.
I am also deeply indebted to Dr Janette Watson who took the burden to read and
comment an earlier draft of this manuscript. Her comments helped to significantly im-
prove the quality of the final manuscript.
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