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59
Received: 4 July 2016; Accepted: 10 Oct 2016; Published online: 5 December 2016
Crustacean Research 2016 Vol.45: 59–67
©Carcinological Society of Japan. doi: 10.18353/crustacea.45.0_59
A new species and new host records of the genus Elthusa
(Crustacea: Isopoda: Cymothoidae) from Japan
Nobuhiro Saito, Takeo Yamauchi
Abstract. ̶Elthusa moritakii sp. nov., a branchial parasite of the deepwater bullhead
sculpin Ereunias grallator, is described from Japan. The new species is morphologi-
cally similar to Elthusa propinqua (Richardson, 1904), but can be distinguished from
the congener by a combination of characteristics of ovigerous females, including pe-
reopods 5–7 with unexpanded carina, number of robust setae on maxilla, greatest
width of pleon, shape of pleopods, and length of pleotelson. Further, new host records
of E. propinqua are here reported. This species was recently collected from five mac-
rourid fish species from Japan, including the grenadiers, Coelorinchus jordani, C. lon-
gissimus, the spearnose grenadier, C. multispinulosus, the unicorn grenadier, C. pro-
ductus, and the Sagami grenadier, Ventrifossa garmani.
Key words: Cymothoidae, Elthusa moritakii sp. nov., Elthusa propinqua, Ereunias grallator, new
host record, Macrouridae
■Introduction
The genus Elthusa Schioedte & Meinert,
1884 (Crustacea: Isopoda: Cymothoidae) com-
prises 28 species in the world (Bruce &
Schotte, 2016), infesting mainly buccal or
branchial cavities of marine fishes (Bruce,
1990). The following five species have been
recorded from Japan (Richardson, 1909; Shii-
no, 1951; Saito et al., 2000; Yamauchi, 2009,
2016); E. caudata (Schioedte & Meinert,
1884), E. propinqua (Richardson, 1904), E.
raynaudii (H. Milne Edwards, 1840), E. sacci-
ger (Richardson, 1909), and E. samariscii
(Shiino, 1951).
Through our studies on Japanese isopods,
some cymothoid specimens were collected
from the deepwater bullhead sculpin, Ereunias
grallator Jordan & Snyder, 1901, from Japan.
Examination of the specimens revealed that it
was an undescribed species of Elthusa, closely
related with Elthusa propinqua. In this report,
we describe it as a new species.
Elthusa propinqua was previously recorded
from some macrourid fish from Japan, the Phil-
ippines, India, and Australia (Richardson,
1909; Barnard, 1936; Bruce, 1990). However,
these host fish specimens had not be identified
to species level. Our examination of specimens
of E. propinqua has shown that this isopod was
found from five fish species from Japanese wa-
ters. All of these fish are new host records for
E. propinqua, which we report here.
■Materials and Methods
Specimens of isopods and fish were pre-
served in 70% ethanol. Observations of mor-
phological characters were made under a
binocular microscope (Olympus X-II).
Measurements and drawings were made with
the aid of an Olympus BHB-Tr microscope
equipped with a drawing tube. Body lengths of
the isopods were measured from the tip of the
cephalon to the posterior end of the pleotelson
along the dorsal mid line. Other measurements
NOBUHIRO SAITO, TAKEO YAMAUCHI
60 Crustacean Research 45 Crustacean Research 45
and terminologies essentially follow those used
by Bruce (1986) for the cymothoid, and Naka-
bo (2013) for the host fishes. The specimens of
the new species and Elthusa propinqua are de-
posited in the Museum of Nature and Human
Activities, Hyogo, Japan; the Osaka Museum
of Natural History, Osaka, Japan; and the Kita-
kyushu Museum of Natural History and Hu-
man History, Kitakyushu, Japan.
List of abbreviations: BL, body lengths;
KMNH, the Kitakyushu Museum of Natural
History and Human History, Kitakyushu,
Japan; MNHA, the Museum of Nature and
Human Activities, Hyogo, Japan; OMNH, the
Osaka Museum of Natural History, Osaka,
Japan; RS, robust seta/e.
■Taxonomic Account
Family Cymothoidae Leach, 1818
Genus Elthusa Schioedte & Meinert, 1884
Elthusa moritakii sp. nov.
(Figs. 1–5)
[New Japanese name: Torikajika-eramoguri]
urn:lsid:zoobank.org:act:87A97DC7-B49D-
43D7-B9B2-4783F52AFBCC
Material examined
Holotype: East China Sea. KMNH IvR
500,847, 1 ovig. female (31.6 mm BL), ex.
branchial cavity of Ereunias grallator collected
from R/V Nagasaki-Maru, Nagasaki Univer-
sity, cruise N211, west of Amakusa-nada Ba-
sin, St-A6 (32°08′62″N, 129°29′26″E), 513 m
depth, 10 May 2006.
Paratypes: North Pacific Ocean. MNHA-A
2013243, 1 non-ovig. female (30.0 mm BL),
ex. right branchial cavity of E. grallator
(157 mm TL), Suruga Bay (unknown advanced
data); MNHA-A2013244–2013247, 1 non-
ovig. female (30.7 mm BL), ex. right branchial
cavity of host fish; 1 male (18.0 mm BL), ex.
left branchial cavity of host fish; 2 males (10.6
and 8.2 mm BL), ex. base of left pectoral fin
and surface of lower jaw of E. grallator
(270 mm SL), off Mikizaki, Owase, Mie Pre-
fecture (33°58′53″N, 136°22′00″E), about
300 m depth, 9 Jan. 2015, coll. T. Moritaki.
East China Sea. KMNH IvR 500,848–
500,850, 1 non-ovig. female (29.5 mm BL),
and 2 males (16.4, 13.9 mm BL), ex. E. gralla-
tor caught by R/V Nagasaki-Maru, Nagasaki
University, cruise N251, St-M (31°35.54′N,
128°28.21′E̶31°36.89′N, 128°28.26′E), 533 m
depth, 14 Nov. 2007; KMNH IvR 500,851–
500,855, 1 non-ovig. female (34.5 mm BL),
and 4 males (15.6, 8.5, 8.0, 7.7 mm BL), ex. E.
grallator caught by R/V Nagasaki-Maru,
Naga saki University, cruise N275, St-A (32°
09.81′N, 129°27.98′E), 497 m depth, 3 Dec.
2008.
Description of holotype female (Figs. 1–4)
Body ovate, weakly twisted, 2.2 times as
long as wide, greatest width at pereonite 4;
dorsum weakly vaulted, dorsal surface smooth.
Cephalon triangular, deeply immersed in pe-
reonite 1; frontal margin subacute; posterior
margin not trilobed. Eyes small, trapezoid, nar-
row.
Pereonite 1 anterolateral margins produced,
forming rounded lobes; pereonites 3 and 4 dis-
tinctly longer than other somites; posterior
margin of pereonite 7 deeply concave, postero-
lateral margins produced, forming rounded
lobes. Coxae 2 to 4 partly or totally concealed
by preceding pereonites in dorsal view, pos-
teroventral angles rounded.
Pleon greatest width 0.7 times as wide as
greatest body width; pleonite 1 narrower than
2, distinctly shorter than other pleonites; pos-
terolateral angles of pleonite 5 convex.
Pleotelson semicircular, 0.6 times as long as
greatest width.
Antennule bases separated; reaching beyond
posterior of cephalon; composed of 8 articles.
Antenna reaching beyond mid-point of pere-
onite 1; composed of 11 articles.
Mandible palp composed of 3 articles; article
2 with 3 short setae; article 3 with 1 RS and 3
A NEW SPECIES OF THE GENUS ELTHUSA
61
Crustacean Research 45 Crustacean Research 45
short setae; apical incisor acute, molar obscurity.
Maxillule with 4 RS at tip.
Maxilla rectangular, with 2 RS each on mesi-
al and lateral lobe.
Maxilliped produced expanded oostegital
lobe; article 3 with 3 hooked terminal RS.
Pereopod 1 basis oblong, without carina on
superior margins; ischium, 0.7 times as long as
basis; merus, 0.5 times as long as ischium; car-
pus 0.3 times as long as merus; propodus sub-
equal to combined lengths of merus and car-
pus; dactylus 0.7 times as long as propodus,
recurved. Basis of pereopods 5 to 7 with week
carina.
Pleopods all lamellar, surface smooth. Pleo-
pod 1 peduncle 2.3 times as wide as length; en-
dopod rectangular, 2.0 times as long as width;
exopod elliptical, lateral margin almost
straight, 1.7 times as long as width. Pleopod 2
similar to pleopod 1. Pleopods 3 to 5 exopod
ovate.
Uropod peduncle trapezoidal; endopod ellip-
tical, 1.9 times as long as greatest width; exo-
pod longer than endopod, 2.2 times as long as
exopods greatest width. Each uropodal ramus
extending to mid-point of pleotelson.
Description of paratype male (Fig. 5)
Body symmetrical, 2.1 times as long as
greatest width, lateral margins subparallel. An-
terolateral margins of pereonite 1 not forming
produced lobes. Antenna reaching beyond mid-
point of pereonite 3. Pleopod 2 with appendix
masculine, reaching beyond about 75% of en-
Fig. 1. Elthusa moritakii sp. nov., holotype, ovig. female (31.6 mm BL), KMNH IvR 500,847, ex. branchial cavity of Ereunias
grallator. A, dorsal view; B, left lateral view; C, cephalon and pereonite 1, dorsal view; D, frons with right antenae, ventral view.
NOBUHIRO SAITO, TAKEO YAMAUCHI
62 Crustacean Research 45 Crustacean Research 45
dopod. Pleotelson length 0.7 times as long as
width. Uropod nearly extending pleotelson
posterior margin.
Coloration
Alcohol-preserved specimens appear pale
yellow or whitish, without chromatophores;
eye color black or light brown.
Distribution
Known only from bathyal zones at depths of
300–500 m of the Pacific coast of Honshu and
East China Sea coast of Kyushu, Japan.
Ecological note
All three captured deepwater bullhead scul-
pin from off Owase on 9 January 2015 were
infested by this species. One of these fish spec-
imens was infested with four E. moritakii; a
non-ovig. female (MNHA-A2013244) and a
male (MNHA-A2013245) on both of the right
and left branchial cavities, respectively, and
two small males (MNHA-A2013246 and
A2013247) attaching to the base of the pectoral
fin and the surface of the lower jaw. The site
specificity of the small males are irresolute as
they may have crawled out from the branchial
cavities of the dead host prior to being brought
to the laboratory. The other two fish specimens
were infested by one or two specimens of E.
moritakii in both right and left branchial cavi-
ties.
Etymology
The name is dedicated to the collector of the
cymothoid specimens, Mr. Takeya Moritaki.
Fig. 2. Elthusa moritakii sp. nov., holotype, ovig. female (31.6 mm BL), KMNH IvR 500,847. All mouthparts dissected from
right side from the dorsal view. A, mandible; B, apex of mandibular palp; C, maxillule; D, magnified maxillule apex; E, maxilla;
F, magnified maxilla apex; G, maxilliped; H, magnified maxilliped article 3.
A NEW SPECIES OF THE GENUS ELTHUSA
63
Crustacean Research 45 Crustacean Research 45
Remarks
A revised diagnosis of the genus Elthusa was
presented by Bruce (1990). The following
morphological characteristics of Elthusa mori-
takii sp. nov. well agree with the generic char-
acteristics of Elthusa in most of the diagnostic
aspects; the weakly vaulted body shape, cepha-
lon posterior margin not trilobed, a usually
wide pleon, antennule shorter than antenna,
and pleopods lamellar. Elthusa moritakii (fe-
male) is most similar to E. propinqua rede-
scribed in detail by Bruce (1990). Both species
have the weakly twisted ovate body, weakly
vaulted dorsum; anterolateral margins of pere-
onite 1 produced rounded lobes; long antenna,
reaching beyond mid-point of pereonite 1.
However, the new species can be differentiated
from E. propinqua in having carina on basis of
pereopods (unexpanded, on pereopods 5–7 in
E. moritakii vs. expanded, on pereopods 4–7 in
E. propinqua), number of RS on each of mesial
and lateral lobes of maxilla (2 RS in E. morita-
kii vs. 1 in E. propinqua), greatest width of
pleon (0.7 times as wide as greatest body width
in E. moritakii vs. 0.86 times in E. propinqua),
shape of pleopodal exopods (elliptical in E.
Fig. 3. Elthusa moritakii sp. nov., holotype, ovig. female (31.6 mm BL), KMNH IvR 500,847. A–G, pereopods 1 to 7, respectively
(right).
NOBUHIRO SAITO, TAKEO YAMAUCHI
64 Crustacean Research 45 Crustacean Research 45
moritakii vs. approximately circular in E. pro-
pinqua), and pleotelson (0.6 times as long as
wide in E. moritakii vs. 0.46 times in E. pro-
pinqua).
Elthusa moritakii can be easily separated
also from the other four Japanese species by
their characteristics of body symmetry, cepha-
lon shapes, and basis of pereopods 6–7 (see
Table 1). Furthermore, these Japanese species
including E. moritakii are each known to infest
different host fishes.
Elthusa propinqua (Richardson, 1904)
[Japanese name: Sokodara-eramoguri]
Material examined
North Pacific Ocean. OMNH Ar5266, 1
ovig. female (23.0 mm BL), ex. branchial cavi-
ty of Ventrifossa garmani (Jordan & Gilbert,
1904) (OMNH P10030), off Kuno (138°
31′10″E 34°53′55″N), Suruga Bay, 250–590 m
depth, 8 Oct. 1996, coll. K. Hatooka; MNHA-
A2013248, 1 ovig. female (20.0 mm BL), ex. V.
Fig. 4. Elthusa moritakii sp. nov., holotype, ovig. female (31.6 mm BL), KMNH IvR 500,847. A–E, pleopods 1 to 5, respectively
(right); F, uropod (right).
A NEW SPECIES OF THE GENUS ELTHUSA
65
Crustacean Research 45 Crustacean Research 45
garmani, off Fukude, Iwata, 300–350 m depth,
23 May 2003, coll. F. Ôe; MNHA-A2013249,
1 ovig. female (22.3 mm BL), ex. V. garmani
(233 mm TL), off Heda, Numazu, Suruga Bay,
200–400 m depth, 22 Nov. 2006, coll. Y. Suzu-
ki; MNHA-A2013250, 1 ovig. female
(18.0 mm BL), ex. V. garmani (258 mm TL),
off Heda, Numazu, Suruga Bay, 200–400 m
depth, 22 Nov. 2006, coll. Y. Suzuki; MNHA-
A2013251, 1 ovig. female (13.0 mm BL), ex.
Coelorinchus jordani Smith & Pope, 1906
(60 mm preanal length), off Heda, Numazu,
Suruga Bay, 200–400 m depth, 22 Nov. 2006,
coll. Y. Suzuki; MNHA-A2013252, 1 male
(8.0 mm BL), ex. Coelorinchus multispinulo-
sus Katayama, 1942 (65 mm preanal length),
off Heda, Numazu, Suruga Bay, 200–400 m
depth, 22 Nov. 2006, coll. Y. Suzuki; MNHA-
A2013253, 1 ovig. female (19.0 mm BL), ex.
C. multispinulosus (251 mm TL), off Heda,
Fig. 5. Elthusa moritakii sp. nov., paratype, male (18.0 mm BL), MNHA-A2013245, ex. left branchial cavity of Ereunias grallator
(270 mm SL). A, dorsal view; B, pleopod 2 (right).
Table 1. Comparison of the characteristics of species of the genus Elthusa in Japan.
Body symmetry Cephalon Basis of
pereopods 6–7 Reference
Elthusa caudata nearly symmetrical deeply immersed in pereonite 1 with carina Schioedte & Meinert (1884), Thieleman (1910)
E. moritakii sp. nov. weakly twisted deeply immersed in pereonite 1 unexpanded Present study
E. propinqua weakly twisted deeply immersed in pereonite 1 with carina Richardson (1904), Bruce (1990)
E. raynaudii nearly symmetrical moderately immersed in pereonite 1 with carina Bruce (1990)
E. sacciger nearly symmetrical deeply immersed into pereonite 1 with carina Bruce (1990), Yamauchi (2009)
E. samariscii weakly twisted weakly immersed in pereonite 1 unexpanded Shiino (1951), Kumar & Bruce (1997)
NOBUHIRO SAITO, TAKEO YAMAUCHI
66 Crustacean Research 45 Crustacean Research 45
Numazu, Suruga Bay, 200–400 m depth, 22
Nov. 2006, coll. Y. Suzuki; MNHA-
A2013254–2013277, 15 ovig. females (21.0–
16.0 mm BL), 7 non-ovig. females (19.5–
17.0 mm BL), and 2 males (18.5, 8.0 mm BL),
ex Coelorinchus longissimus Matsubara, 1943,
off Minamiise, Mie Prefecture, 240–290 m
depth, 29 Oct. 2015, coll. T. Moritaki; MNHA-
A2013565–2013568, 4 non-ovig. females
(14.0, 15.0, 15.0, 17.0 mm BL), ex. branchial
cavities of Coelorinchus productus Gilbert &
Hubbs, 1916 (195, 220, 225, 235 mm TL), off
Heda, Numazu, Suruga Bay, 25 Apr. 2016,
coll. T. Saruwatari; MNHA-A2013278, 1 ovig.
female (19.0 mm BL), host unknown, Suruga
Bay, 400–500 m depth, 2 Nov. 2004, coll. S.
Tsuzuki.
Remarks
Elthusa propinqua was previously recorded
from chalinura fish from Japan and a macru-
rid fish, Macrurus and Ventrifossa cf. ni-
grodorsalis from the Philippines, India, and
Australia (Richardson, 1909; Barnard, 1936;
Bruce, 1990). The present study increases the
number of new host records for Japanese mac-
rourid fishes parasitized by E. propinqua: the
grenadiers Coelorinchus jordani Smith &
Pope, 1906, C. longissimus Matsubara, 1943,
the spearnose grenadier C. multispinulosus Ka-
tayama, 1942, the unicorn grenadier C. produc-
tus Gilbert & Hubbs, 1916, and the Sagami
grenadier Ventrifossa garmani (Jordan & Gil-
bert, 1904). The infestation prevalence of E.
propinqua on C. longissimus was 15.4% (n＝
117 fishes) in this study.
The general characteristics of the specimens
collected in this study corresponded to the re-
description of E. propinqua (Bruce, 1990).
■Acknowledgements
We wish to express our gratitude to Mr T.
Moritaki (Toba Aquarium), Dr T. Saruwatari
(University of Tokyo), Associate Professor M.
Moriguchi (Okinawa University), Mr S. Tsuzu-
ki (Chiba City), and Mr T. Shimizu and Mr Y.
Suzuki (Nihon University) for providing speci-
mens and valuable information. We are also
much indebted to Dr M. Shimomura (Kitaky-
ushu Museum of Natural History and Human
History), and Dr R. Yamanishi and Mr K. Ha-
tooka (Osaka Museum of Natural History) for
the loan of some materials of the museum col-
lection. We sincerely thank to Dr B.A. Ven-
mathi Maran (Kyungpook National University)
and Dr S. Dunbar (Loma Linda University) for
making helpful suggestions concerning early
drafts of this paper. Thanks are also extended
to Dr A. Asakura (Kyoto University) and two
anonymous reviewers for their reviewing this
manuscript. Part of the present study was sup-
ported by Grant-in-Aids for Scientific Research
(B) (No. 15K21298 to TY) from the Japan So-
ciety for the Promotion of Science.
■Literature Cited
Barnard, K. H., 1936. Isopods collected by the
R.I.M.S. Investigator. Records of the Indi-
an Museum, 38: 147–191.
Bruce, N. L., 1986. Revision of the isopod crus-
tacean genus Mothocya Costa, in Hope,
1851 (Cymothoidae: Flabellifera), parasitic
on marine fishes. Journal of Natural History,
20: 1089–1192.
Bruce, N. L., 1990. The genera Catoessa, Elthu-
sa, Enispa, Ichthyoxenus, Idusa, Livoneca
and Norileca n. gen., (Isopoda, Cymothoi-
dae), crustacean parasites on marine fishes,
with descriptions of eastern Australian spe-
cies. Records of the Australian Museum, 42:
247–300.
Bruce, N. L., & Schotte, M., 2016. Elthusa
Schioedte & Meinert, 1884. In: M. Schotte,
C. B. Boyko, N. L. Bruce, G. C. B. Poore, S.
Taiti, & G. D. F. Wilson, (eds.), World Ma-
rine, Freshwater and Terrestrial Isopod
Crustaceans Database. Accessed through:
World Register of Marine Species at http://
www.marinespecies.org/aphia.php?p=tax
A NEW SPECIES OF THE GENUS ELTHUSA
67
Crustacean Research 45 Crustacean Research 45
details&id=118410 on 2016-05-20.
Kumar, A. B., & Bruce, N. L., 1997. Elthusa
samariscii (Shiino, 1951) (Isopoda, Cymo-
thoidae) parasitizing Samaris cristatus
Gray, 1831, off the Kerala coast, India.
Crustaceana, 70: 780–787.
Nakabo, T. (ed.), 2013. Fish of Japan with Picto-
rial Keys to the Species, Third Edition [in 3
volumes]. xlix＋xxxii＋xvi＋2428 pp, To-
kai University Press, Hadano.
Richardson, H., 1904. Contributions to the natu-
ral history of the Isopoda. Proceedings of
the United States National Museum, 27:
1–89.
Richardson, H., 1909. Isopods collected in the
northwest Pacific by the U.S. bureau of fish-
eries steamer Albatross in 1906. Proceed-
ings of the United States National Museum,
37 (1701): 75–129.
Saito, N., Itani, G., & Nunomura, N., 2000. A
preliminary check list of isopod crustaceans
in Japan. Bulletin of the Toyama Science
Museum, 23: 11–107. (in Japanese with
English abstract)
Schioedte, J. C., & Meinert, F. W., 1884. Symbolae
ad Monographiam Cymothoarum Isopodum
Familiae 4. Cymothoidae. Trib. II. Cymothoi-
nae. Trib. III. Livonecinae. Naturhistorisk
Tidsskrift (3) 14: 221–454.
Shiino, S. M., 1951. On the cymothoid Isopoda
parasitic on Japanese fishes. Bulletin of the
Japanese Society of Scientific Fisheries, 16:
81–89. (in Japanese with English abstract)
Thielemann, M., 1910. Beiträge zur Kenntnis der
Isopodenfauna Ostasiens. Abhandlungen.
Akademie der Wissenschaften Mathe-
matischen-Physikalische Klasse in München,
2(3): 1–109.
Yamauchi, T., 2009. Deep-sea cymothoid isopods
(Crustacea: Isopoda: Cymothoidae) of Pacif-
ic coast of northern Honshu, Japan. National
Museum of Nature and Science Mono-
graphs, 39: 467–481.
Yamauchi, T., 2016. Cymothoid isopods (Isopo-
da: Cymothoidae) from fishes in Japanese
waters. Cancer, 25: 113–119. (in Japanese
with English title)
Addresses
(NS) Suido-sha Co. Ltd., Ikuta 8–11–11, Tama-
ku, Kawasaki, Kanagawa 214–0038, Japan;
(TY) Institute of National and Environmental
Sciences, University of Hyogo/Museum of
Nature and Human Activities, Hyogo, Yayoiga-
oka 6, Sanda, Hyogo 669–1546, Japan
E-mail addresses
(NS)* nsaitoh@suidosha.co.jp
(TY) cymothoid@yahoo.co.jp
*Corresponding author
