Morphological features and systematic position of the bryozoans Onychocella rowei and O. mimosa (Cheilostomata) from a Campanian erratic block (Belarus)

Abstract

The results of the investigations into the morphology of two bryozoan species Onychocella rowei (Brydone, 1906) and O. mimosa Brydone, 1930 (Cheilostomata: Onychocellidae Jullien, 1881) the specimens of which were discovered in an erratic block of Campanian age located in the vicinity of the town of Grodno (Belarus) are presented. The intra- and intercolonial variability of avicularia of these species are studied. Some colonies of O. rowei are shown to be aberrant forms that exhibit various developmental anomalies of autozooids and avicularia. Some specimens of O. rowei are shown to have reparative avicularia. The taxonomic positions of these species are discussed.

Full text

ISSN 00310301, Paleontological Journal, 2014, Vol. 48, No. 3, pp. 275–286. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © A.V. Koromyslova, 2014, published in Paleontologicheskii Zhurnal, 2014, No. 3, pp. 57–66.
275
INTRODUCTION
This paper is the first to describe in detail the mor
phology of bryozoans
Onychocella rowei
(Brydone,
1906) and
O. mimosa
Brydone, 1930 (Cheilostomata:
Onychocellidae Jullien, 1881) that were uncovered
from an erratic block of Campanian age located in the
vicinity of Grodno (Belarus). The type material of
these species comes from the upper Campanian–
lower Maastrichtian (
Ostrea lunata
Zone) of England
(Brydone, 1906, 1913, 1930) and is reposited at the
Sedgwick Museum of Earth Sciences, University of
Cambridge. Both species have wide stratigraphic and
geographic distributions:
O. rowei
is known from the
Middle Coniacian–upper Maastrichtian of north
western Europe (Schubert, 1986), upper Campanian
of Uzbekistan (Favorskaya, 1996), and the upper
Campanian and upper Maastrichtian of Turkmenistan
(Voigt, 1967);
O. mimosa
is known from the Maas
trichtian of northwestern Europe (Schubert, 1986),
lower Maastrichtian of Uzbekistan (Favorskaya,
1996), and the upper Maastrichtian of Turkmenistan
(Voigt, 1967). The type material of
O. rowei
and
O. mimosa
(Brydone, 1906, 1913, 1930) and speci
mens of these species from the above localities were
described very briefly (Voigt, 1967; Schubert, 1986). In
T.A. Favorskaya’s paper (1996) these species were
listed without any description. It is projected that in
the future the morphology of the type specimens and
colonies of these species from all known localities will
be investigated in detail in order to either confirm their
placement in these species or place them in other spe
cies. In addition, it is noteworthy that the morpholog
ical features of avicularia of
O. rowei
and
O. mimosa
,
are of particular interest because they underlie the dif
ferences between the bryozoans of these species and
the majority of other members of the genus
Onycho
cella
Jullien, 1881.
MATERIAL AND METHODS
This research is based on the examination of frag
ments of bryozoan colonies of
O. rowei
(about 35 spec
imens) and
O. mimosa
(two specimens). They come
from the quarry in the vicinity of Grodno that was
developed by the Grodno Building Materials Plant.
The quarry exposed an erratic block from which to
date have been studied some bryozoans of the order
Tubuliporida (Viskova, 2000, 2004),
Bicavea fungifor
mis
(Hagenow, 1846),
Discofascigera ternata
Viskova,
2000, and
Idemona occultata
Viskova, 2004, and
belemnitellids (Barskov and Weiss, 1987),
Belemnitella
mucronata
Schlotheim, 1813; based on these belemni
tellids the supposed age of the erratic block has been
estimated as Campanian. In the region of Grodno the
bedrock Campanian deposits are overlain by Maas
trichtian deposits, which are overlain by Paleogene or
Anthropogene formations (Makhnach et al., 2001).
No bryozoans have been reported yet from any bed
rock deposits of the Campanian of Belarus.
Morphological Features and Systematic Position of the Bryozoans
Onychocella rowei
and
O. mimosa
(Cheilostomata)
from a Campanian Erratic Block (Belarus)
A. V. Koromyslova
Borissiak Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya ul. 123, Moscow, 117997 Russia
email: koromyslova.anna@mail.ru
Received February 13, 2013
Abstract
—The results of the investigations into the morphology of two bryozoan species
Onychocella rowei
(Brydone, 1906) and
O. mimosa
Brydone, 1930 (Cheilostomata: Onychocellidae Jullien, 1881) the specimens
of which were discovered in an erratic block of Campanian age located in the vicinity of the town of Grodno
(Belarus) are presented. The intra and intercolonial variability of avicularia of these species are studied.
Some colonies of
O. rowei
are shown to be aberrant forms that exhibit various developmental anomalies of
autozooids and avicularia. Some specimens of
O. rowei
are shown to have reparative avicularia. The taxo
nomic positions of these species are discussed.
Keywords
: Bryozoa, Campanian, erratic block, morphology, colonial variability, aberrant forms, reparative
avicularia, taxonomy
DOI: 10.1134/S0031030114030137

276
PALEONTOLOGICAL JOURNAL Vol. 48 No. 3 2014
KOROMYSLOVA
The collection of bryozoans was assembled in the
1980s by A.F. Weiss, a former member of the Borissiak
Paleontological Institute of the Russian Academy of
Sciences (PIN). The author examined all colonies of
O. rowei
and
O. mimosa
using the scanning electron
microscope Tescan Vega XMU. The following ele
ments of the colonies have been selected and mea
sured (Fig. 1): (AvL) avicularium length; (AvW) width
of avicularium; (AzL) length of autozooecium; (AzW)
width of autozooecium; (ARL) length of the apex of
the rostrum of avicularium overlapping the proximal
part of the distal autozooecium; (CrOOL) length of
the cryptocyst of avicularium occupied by an opesium
and opesiules; (CrOOW) width of the cryptocyst of
avicularium occupied by an opesium and opesiules;
(OpL) length of the opesium of autozooecium without
an ooecium; (OpW) width of the opesium of autozoo
ecium without an ooecium; (OpOL) length of the ope
sium of autozooecium with an ooecium; (OpOW)
width of the opesium of autozooecium with an
ooecium; (PrL) length of the proximal part of avicu
larium; and (RL) length of the rostrum of avicularium.
The length of autozooecia with ooecia has been
measured from the upper boundary of the ooecium sep
arating it from the distal autozooecium (Figs. 1a, 1b),
and the length of autozooecia without ooecia has been
measured from the edge of the distal wall of the auto
zooecium to its proximal wall (Fig. 1d). In order to
compare the autozooecia with different shapes (piri
form and ovate) more adequately their widths have
been measured at the level of the base rather than in
the widest part of opesia (Figs. 1a, 1b, 1d). The length
of the opesia with ooecia has been measured from the
upper edge of ooecium to the proximal edge of ope
sium (Fig. 1b), and the length of opesia without ooecia
has been measured from the distal edge of opesium to
its proximal edge (Fig. 1c). In
O. rowei
the width of
opesia has been measured between the lateral projec
tions (Fig. 1c), and in
O. mimosa
it has been measured
at the level of the center of opesium (Pl. 10, fig. 2c).
The length of the rostrum of avicularium has been
measured from the end of its apex to the lower subcir
cular opesiule, not including the latter (Fig. 1c). The
measurements of the colonies of bryozoans
O. rowei
and
O. mimosa
are presented in Table 1.
Fig. 1.
Measurements of main elements of the colonies of
Onychocella rowei
(Brydone, 1906); (a, b) specimen PIN, no. 2922/210:
(a) length and width measurements of the piriform autozooecium with an ooecium (arrow indicates the ooecium) and avicular
ium and the frontal surface of the avicularium occupied by an opesium and opesiules; (b) length and width measurements of the
ovate autozooecium with an ooecium and the opesium of a piriform autozooecium with an ooecium (arrows indicate the ooecia);
(c) specimen PIN, no. 2922/201, length measurements of the rostrum, apex of the rostrum, and the proximal part of the avicu
larium and the length and width measurements of the opesium of a piriform autozooecium without an ooecium (arrow indicates
the mandible attachment site); (d) specimen PIN, no. 2922/234, length and width measurements of the piriform and ovate auto
zooecia without an ooecia. See the Material and Methods section for designations. Scale bars: (a, c) 200
µ
m, (b, d) 500
µ
m.
AvL
AvW
AzW
AzL
CrOOL
CrOOW
AzW
AzL
OpOL
OpOW
RL
PrL
OpL
OpW
ARL
AzW
AzL
AzW
AzL
(a) (b)
(c) (d)

PALEONTOLOGICAL JOURNAL Vol. 48 No. 3 2014
MORPHOLOGICAL FEATURES AND SYSTEMATIC POSITION OF THE BRYOZOANS 277
Table 1.
Measurements (in mm) of the main elements of autozooecia and avicularia of
Onychocella rowei
(Brydone, 1906) and
Onychocella mimosa
Brydone, 1930
Elements
measured
Onychocella rowei Onychocella mimosa
colonies of group 1 colonies of group 2 colonies of group 3 colonies of group 2
autozooecia
avicularia
autozooecia
avicularia
autozooecia
avicularia
autozooecia
avicularia
piriform ovate piriform ovate piriform ovate piriform ovate
Autozooecia
AzL 0.58–0.91 0.59–0.92 0.55–0.94 0.51–0.83 0.75–0.96 0.65–0.80 0.62–0.82 0.69–0.81
AzW 0.29–0.39 0.33–0.44 0.30–0.49 0.36–0.44 0.35–0.41 0.39–0.53 0.29–0.38 0.34–0.37
OpL 0.25–0.38 0.25–0.45 0.26–0.33 0.25–0.33 0.27–0.34 0.27–0.32 0.21–0.28 0.19–0.21
OpW 0.22–0.24 0.19–0.27 0.19–0.27 0.19–0.24 0.19–0.25 0.20–0.27 0.16–0.22 0.19–0.21
OpOL 0.33–0.44 0.33–0.45 0.36–0.41 0.38–0.41 0.40–0.41 0.41 0.24–0.29 0.28–0.34
OpOW 0.22–0.26 0.21–0.28 0.26–0.28 0.25–0.27 0.22–0.26 0.25 0.21–0.24 0.24–0.25
Avicularia
AvL 0.82–1.05 0.66–1.05 0.74–0.92 0.76–1.00
AvW 0.25–0.32 0.22–0.34 0.28–0.34 0.26–0.34
ARL 0.56–0.73 0.40–0.66 0.44–0.56 0.41–0.63
RL 0.15–0.21 0.00–0.13 absent 0.00–0.13
PrL 0.24–0.39 0.24–0.43 0.30–0.36 0.30–0.43
CrOOL 0.18–0.31 0.19–0.27 0.21–0.28 0.18–0.23
CrOOW 0.07–0.09 0.07–0.12 0.09–0.13 0.06–0.10

278
PALEONTOLOGICAL JOURNAL Vol. 48 No. 3 2014
KOROMYSLOVA
The collection under consideration is reposited at
the Laboratory of Higher Invertebrates, Borissiak
Paleontological Institute, Russian Academy of Sci
ences (PIN), no. 2922.
MORPHOLOGICAL FEATURES
OF BRYOZOANS UNDER CONSIDERATION
The colonies of bryozoans
O. rowei
(Pl. 9; Figs. 1–4)
and
O. mimosa
(Pl. 10) are erect bilateral, multiserial,
from 2.0 to 10.0 mm in size; they were formed by the
more or less simultaneous backtoback growth of
zooids. The ancestrula has not been preserved, and the
early astogenetic stage is not known. The colonies
consist of piriform and ovate autozooecia and vicari
ous avicularia. The autozooids always budded distally,
and the avicularia always budded distolaterally
(Fig. 2). The vertical growth of colonies was due to
piriform autozooids that formed vertical rows (lineal
series, according to Lidgard, 1985), and the horizontal
growth was due to ovate autozooids and avicularia that
formed horizontal rows. The avicularia budding off
from autozooids gave rise to new vertical rows. From
these avicularia ovate autozooids were budded distally,
from which in turn piriform autozooids were budded.
This budding pattern of zooids ensures the arrange
ment of ovate autozooecia and avicularia relative to
piriform autozooecia characteristic of
O. rowei
and
O. mimosa
(Fig. 2, portion of the colony within the
rim): if one of the horizontal rows contains an ovate
autozooecium and avicularium that are respectively
located left and right of a piriform autozooecium, then
the next horizontal row contains an avicularium and
ovate autozooecium that are respectively located left
and right of a piriform autozooecium, subsequently
this sequence repeats itself. In addition to this arrange
ment, some specimens could contain the following
sequence (Fig. 2, portion of the colony right of the
rim): if one of the horizontal rows contains avicularia
left and right of a piriform autozooecium, then the
next horizontal row contain ovate autozooecia left and
right of a piriform autozooecium, subsequently this
sequence repeats itself.
Autozooecia.
The piriform autozooecia have a nar
row proximal end and widened distal end. The widen
ing usually starts from the proximal margin of the ope
Fig. 2.
Scheme of zooidal budding in colonies of
Onychocella rowei
(Brydone, 1906); specimen PIN, no. 2922/210, general
appearance of the erect bilateral colony. Designations: thin white arrows indicate the distolateral budding of avicularia, thick
black arrows indicate the distal budding of ovate autozooids from avicularia, thick white arrows indicate the distal budding of pir
iform autozooids from ovate and piriform autozooids; vertical dashes indicate ovate autozooecia, horizontal dashes indicate avic
ularia. Scale bar 1 mm.

PALEONTOLOGICAL JOURNAL Vol. 48 No. 3 2014
MORPHOLOGICAL FEATURES AND SYSTEMATIC POSITION OF THE BRYOZOANS 279
Fig. 3.
Morphology of avicularia of
Onychocella rowei
(Brydone, 1906); (a) specimen PIN, no. 2922/223, structure of the frontal
surface of avicularium; (b, c) scheme of the longitudinal section of a vicarious avicularium (according to McKinney and Jackson,
1989): (b) avicularium with a functioning polypide, (c) avicularium with a rudimentary polypide. Designations: thick black
arrows indicate opesia, white arrow indicates paired parallel opesiules, gray arrow indicates the orifice, black arrow with a white
contour indicates the mandible attachment site.
200
µ
m
Rostrum
Proximal part
Mandible
Cryptocyst
Membrane
Opesiule for the passage of the abductor
muscle opening the mandible
Polypide Adductor muscle
closing the mandible
(a)
(b) (c)
sium. In ovate autozooecia the proximal end is partly
overlapped by the rostrum of avicularia, and the auto
zooecium begins to widen considerably below the
proximal margin of opesium, usually at the boundary
with an avicularium. The piriform and ovate autozoo
ecia have rounded distal edges (Pls. 9, 10; Figs. 1, 2, 4).
The rim is usually clearly defined (Pl. 9, figs. 1–3, 5–7;
Pl. 10, fig. 2; Figs. 1–3, 4a–4d, 4g, 4h) or, more rarely,
poorly defined (Pl. 9, fig. 4; Pl. 10, fig. 1; Fig. 4e, 4f).
The cryptocyst is slightly granulated, located below
the rim and occupies half or more of the frontal sur
face of autozooecium.
In both species the opesial rim of autozooecia is
formed by a projecting cryptocyst (Pl. 9, figs. 2, 7;
Pl. 10, fig. 2c; Fig. 1d). The opesia of
O. rowei
are ele
vated and are bellshaped because of the small lateral
projections and opesiular indentations, between
which there is a short projection of the cryptocyst, a
little tongue.
O. rowei
has a short tongue (Pl. 9, fig. 2;
Figs. 1c, 2, 4b). It is often broken; in this event the
opesiular indentations are only slightly defined, and
the proximal edge of opesia is almost straight (Pl. 9,
figs. 3, 5, 6; Figs. 1a, 1b, 1d, 2). In the complete
absence of lateral projections and tongue the opesia
are subcircular (Pl. 9, figs. 1, 5).
The opesia of
O. mimosa
are elevated and subcircu
lar. A pair of openings (opesiules) is located 0.07–0.09
mm below them (Pl. 10, figs. 1b–1d, 2b, 2c). It is com
mon knowledge that the opesiular indentations and
opesiules served for the passage of bundles of parietal
muscles. During the formation of opesiular indenta
tions the cryptocyst partly circumscribed the bundles
of muscles and then stopped growing completely,

280
PALEONTOLOGICAL JOURNAL Vol. 48 No. 3 2014
KOROMYSLOVA
Plate 9
1
2
3
4a
5
4b
67

PALEONTOLOGICAL JOURNAL Vol. 48 No. 3 2014
MORPHOLOGICAL FEATURES AND SYSTEMATIC POSITION OF THE BRYOZOANS 281
whereas during the formation of opesiules the crypto
cyst continued growing until the opesiules completely
separated from the opesium (Banta et al., 1997). In
this instance, in
O. mimosa
the cryptocyst (tongue)
and the lateral projections of the opesium fused, which
resulted in the formation of opesiules and in subcircu
lar opesia. It is evident that in
O. mimosa
the fusion of
the lateral projections and the tongue was not com
plete, and in some autozooecia of
O. mimosa
one can
see thin “sutures” running from the opesiules to the
opesium and bordering the tongue on the lateral sides
(Pl. 10, figs. 1d, 2c). In the colonies of
O. mimosa
the
tongue is often partially destroyed, which leads to the
joining of the opesiules and opesia. Thus the opesia of
O. mimosa
are shapes like the opesia of
O. rowei.
In bryozoans of both species zooids communicated
through septulae, which have not been preserved. In
the distal (Pl. 9, fig. 7) and lateral walls of autozooecia
there is a pair of subcircular openings marking their
former positions.
Ovicells
(brood chambers) in
O. rowei
(Pl. 9, figs. 3,
4b, 6; Fig. 1a, 1b, 2) and
O. mimosa
(Pl. 10, figs. 1b, 2b,
2c) were immersed. The brooding cavity was located in
the distal part of the maternal zooid and below the col
ony surface either entirely or largely (Ostrovsky, 2009).
The ooecia (remains of ovicells) are slightly granu
lated, vestigial, and do not protrude above the colony
surface, they usually do not project above the mural
rim of zooecia.
Avicularia.
In bryozoans of these species the mor
phology of avicularia is of greatest interest. The avicu
laria of
O. rowei
(Pl. 9; Figs. 1–4) and
O. mimosa
(Pl. 10, figs. 1a–1c, 2a, 2b) are rhomboidal. Their
frontal surface is divided into the proximal and distal
(rostrum) parts (Figs. 1, 3). The proximal part of avic
ularium is short, frequently have convex lateral sides,
and narrows downward. The rostrum is coneshaped
and symmetrical, mostly with straight lateral walls. At
the base of the rostrum there are dents (Pl. 9, fig. 7;
Figs. 1c, 3a) or projections (Pl. 9, fig. 4; Fig. 4c), these
are lifetime attachment scars of the mandible, which is
not preservable in the fossil record. The entire frontal
surface of avicularium is occupied by a fragile, slightly
granulated cryptocyst, which contains four openings:
two parallel slitlike ones and two subcircular ones, one
at the top and another at the bottom (Pl. 9, fig. 5,
Pl. 10, fig. 2b; Fig. 3a). The cryptocyst between the
openings is frequently destroyed, thus they coalesce
into a single opening of various outlines. Apparently,
the lower opening and two parallel openings are opesi
ules. It is common knowledge that in modern bryozo
ans the opesiule located in the proximal part of the
avicularium serves as a passage for the muscle abduc
tor opening the mandible (McKinney and Jackson,
1989). Probably, these two parallel opesiules could
allow the passage of muscles adductors closing the
mandible (Figs. 3a, 3c). It would appear reasonable
that the upper subcircular opening in the cryptocyst is
an opesium that was located under the orifice (opening
in the membrane) and served as the passage for the ten
tacular crown of the avicularian polypide, if the polyp
ide was developed completely, or for a tuft of sensory
cilia, if the polypide was rudimentary (Figs. 3a–3c)
(Carter et al., 2010a, 2010b).
Reparative avicularia.
The colonies of
O. rowei
yielded reparative avicularia (Pl. 9, fig. 6; Figs. 4g, 4h),
new avicularia with their own wall that originated
inside the old avicularia through either the reparative
budding (reparative budding, according to Banta,
1969) or complete regeneration (total regeneration,
according to Jebram, 1978). No reparative autozooe
cia have been found in the colonies of bryozoans under
consideration. The number of reparative avicularia in
one old avicularium may be as great as three and,
apparently, all of them have the same polarity as the
host avicularium. Reparative budding could occur
both in some (Pl. 9, fig. 6; Fig. 4g) and in all avicularia
of certain colonies (Fig. 4h). It is well known that
reparative zooids originate inside the damaged zooids
devoid of soft body from the septulae of neighboring
zooids. It is suggested that in this way the communica
tion between living zooids was preserved and physio
logical integrity of the colony was maintained (Banta,
1969; Taylor, 1988).
Intra and intercolonial variability.
In the colonies
of
O. rowei
there are three types of avicularia, which in
main parameters are almost identical but differ in the
length of rostrum and rostral apex, which partly over
laps the proximal end of the distal autozooecium
(Table 1).
Type 1
comprises avicularia with long rostra
(0.56–0.73 mm) and long troughlike apices (0.15–
0.21 mm) (Pl. 9, figs. 2, 4a, 5, 6; Figs. 1c, 3a);
type 2
comprises avicularia with short rostra (0.40–0.66 mm)
and short troughlike apices (0.00–0.13 mm) (Pl. 9,
figs. 1, 4b, 7; Figs. 1d, 4c);
type 3
comprises avicularia
with short rostra (0.44–0.56 mm) without projecting
Explanation of Plate 9
Figs. 1–7.
Onychocella rowei
(Brydone, 1906): (1) specimen PIN, no. 2922/200, general appearance of the erect bilateral colony;
(2) specimen PIN, no. 2922/279, avicularium (on the left) and autozooecia (arrow indicates the opesiular indentation); (3) spec
imen PIN, no. 2922/210, avicularium and autozooecium with an ooecium (arrowed); (4) specimen PIN, no. 2922/224: (4a) avic
ularium with a long apex; arrow indicates the mandible attachment site, (4b) avicularia and autozooecia; (5) specimen PIN,
no. 2922/223, two avicularia and autozooecia; (6) specimen PIN, no. 2922/204, autozooecia and avicularia; arrow indicates the
reparative avicularium; (7) specimen PIN, no. 2922/208, autozooecium, avicularium and the distal wall of autozooecium with
two openings that contained septulae; arrows indicate the mandible attachment site and openings in the distal wall. Scale bars:
(1) 1 mm; (4b, 6) 500
µ
m; (2, 3, 4à, 5, 7) 200
µ
m.

282
PALEONTOLOGICAL JOURNAL Vol. 48 No. 3 2014
KOROMYSLOVA
Fig. 4.
Aberrations and reparative avicularia in colonies of bryozoans
Onychocella rowei
(Brydone, 1906); (a–c) specimen PIN,
no. 2922/255: (a) general appearance of the erect bilateral colony, (b) immature autozooecia and avicularia at the edge of the col
ony, (c) abnormal autozooecium between two avicularia; (d) specimen PIN, no. 2922/226, general appearance of the erect bilat
eral colony with deformed autozooecia and avicularia in its central part; (e) specimen PIN, no. 2922/224, autozooecia with an
immature proximal part (arrows indicate); (f) specimen PIN, no. 2922/257, secondarily changed and deformed autozooecia and
avicularia; (g) specimen PIN, no. 2922/223, immature avicularia and autozooecia at the edge of the colony, arrow indicates a
reparative avicularium; (h) specimen PIN, no. 2922/256, autozooecia and reparative avicularia. Designations: black arrows indi
cate autozooecia, white arrows indicate avicularia; (?az) perhaps autozooecium, (?av) perhaps avicularium, (az) autozooecium.
Scale bars: (a, d) 1 mm; (g) 200
µ
m; (b, c, e–h) 500
µ
m.
apices (Pl. 9, fig. 3; Figs. 1a, 1b, 2). On this basis the
specimens under study were divided into three groups.
The first group comprises the colonies in which avicu
laria of type 1 predominate but solitary avicularia of
type 2 may also be present. The second group includes
the colonies in which the avicularia of type 2 predom
inate. These colonies have yielded no avicularia of
type 1, but they may frequently contain avicularia of
type 3. The third group only includes the colonies with
the avicularia of type 3. The second group of colonies is
most common, the first group occurs more rarely, and
the third group is very infrequent (only two specimens).
In all three groups of colonies the ovate and piri
form autozooecia are almost identical in length,
whereas the ovate autozooecia are somewhat wider
than the piriform. In addition, in both types of autozo
oecia the opesia with ooecia are slightly larger than
opesia without ooecia (Table 1).
The colonies of the species
O. mimosa
that have
been examined may be placed in the second group,
since in them the avicularia of type 2 with short rostra
(0.41–0.63 mm) and short troughlike apices (0.00–
0.13 mm) predominate (Table 1; Pl. 10, figs. 1b, 1c, 2b).
The opesia of autozooecia of this species are smaller
than the opesia of
O. rowei
, but just as in the latter spe
cies, the opesia with ooecia are slightly larger than the
opesia without ooecia (Table 1).
Aberrant forms.
The colonies of
O. rowei
have
yielded 13 aberrant forms (1/3 of all colonies under
study), which display various abnormalities in the nor
mal development of autozooids and avicularia
(Figs. 4a–4f). Both the internal (Fig. 4f) and marginal
(Figs. 4a, 4b, 4e, 4g) portions of colonies show accu
mulations of autozooecia in which the opesia are sub
circular and the proximal part is shortened or com
pletely absent and deformed avicularia that are irregu
lar ovate to rhomboidal in shape and possess an
elongated opening at the center. It is obvious that on
the margins of colonies the accumulations of zooecia
with such abnormalities are immature autozooids and
avicularia, whereas in the internal regions of colonies
such accumulations are apparently due to the defor
mation of colonies during their growth (Fig. 4d) or to
some secondary processes, for instance, calcification.
In addition, one of the specimens contains a solitary
deformed autozooecium in which the opesium and
ooecium are displaced to the right margin of the distal
part of the autozooecium (Fig. 4c).
TAXONOMIC POSITION OF BRYOZOANS
UNDER CONSIDERATION
Based on the fact that opesiules evolved in the cryp
tocyst of autozooecia Voigt (1967) and Schubert
(1986) assigned the bryozoans of
Onychocella mimosa
to the genus
Woodipora
Jullien, 1888. The transfer of
this species to the genus
Woodipora
appears to be
unjustified, since in contrast to
O. mimosa
the bryozo
ans of the type species of the genus
Woodipora
—
Flus
tra holostoma
Wood, 1844—have encrusting colonies,
large opesiules located in the central part of the cryp
tocyst of autozooecium, and avicularia with a large
subcircular opesium (Wood, 1844; Busk, 1859).
In addition, Schubert (1986) placed the species
O. rowei
in the genus
Woodipora
. He supposed that ini
tially the opesiular indentations of
O. rowei
were ope
siules and that they resulted from the destruction of
the cryptocyst. On this basis he concluded that
O. rowei
and
O. mimosa
are a single species,
Woodipora
rowei
, the colonies simply differ in the preservation of
opesiules. The author has examined about 35 frag
ments of the colonies of
O. rowei.
And as previously
described, in bryozoans of this species the opesia of
autozooecia are bellshaped because of the small lat
eral projections and opesiular indentations with a
short projecting cryptocystal tongue in between. The
opesia with a straight or rounded proximal edge are
formed in the case when the lateral projections and
cryptocystal tongue are broken off. In addition none of
the specimens yielded autozooecia with subcircular
opesia and opesiules underneath them. Whereas even
in two fragments of colonies of
O. mimosa
they are
observed almost in each autozooecia. As previously
noted, the cryptocyst located between the opesiules in
autozooecia of bryozoans of
O. mimosa
could be
destroyed, and in these cases the opesia took the shape
similar to that of the opesia in colonies of
O. rowei.
Thus, this similarity is only related to the degree of
preservation of colonies. It is quite evident that during
their lifetime the bryozoans of
O. rowei
developed ope
siular indentations and those of
O. mimosa
developed
opesiules. On this basis this paper treats both species as
independent. Furthermore, despite the presence of
opesiules in colonies of
O. mimosa
and opesiular
indentations in
O. rowei
, both species should be con
sidered members of the same genus. It becomes appar
ent that if the autozooecia and avicularia are similar in
morphology, the development of either opesiular
indentations or opesiules in the cryptocyst of autozo

PALEONTOLOGICAL JOURNAL Vol. 48 No. 3 2014
MORPHOLOGICAL FEATURES AND SYSTEMATIC POSITION OF THE BRYOZOANS 283
(a) (b)
(c) (d)
(e) (f)
(g) (h)
?av
az
?az

284
PALEONTOLOGICAL JOURNAL Vol. 48 No. 3 2014
KOROMYSLOVA
Plate 10
1a
2a
1b
2b
1c
1d 2c

PALEONTOLOGICAL JOURNAL Vol. 48 No. 3 2014
MORPHOLOGICAL FEATURES AND SYSTEMATIC POSITION OF THE BRYOZOANS 285
oecia should be treated as a specific rather than
generic character.
As previously discussed, the species
O. rowei
and
O. mimosa
cannot be attributed to the genus
Woodi
pora
. In addition, these morphological features largely
distinguish them from most other species of the genus
Onychocella
. At present, however, the author contin
ues to treat these species as members of the genus
Ony
chocella
because the concept of genus content is too
broad and there is no clear diagnosis (Favorskaya,
1985; Gordon and Taylor, 1999; Schmidt and Bone,
2004; Taylor and McKinney, 2006; Taylor and Gor
don, 2007; Taylor, 2008). On the other hand, in the
structure of autozooecia and avicularia
O. rowei
and
O. mimosa
resemble the bryozoans of
O. strumulosa
(Marsson, 1887) and
O. disparalis
(d’Orbigny, 1851),
which Voigt (1975) also treated as members of the
genus
Woodipora
. Apparently, in the future, when
additional material will be acquired, these four species
may be placed in a separate genus.
CONCLUSIONS
This is the first detailed description of the mor
phology of bryozoans of
Onychocella rowei
and
O. mimosa
uncovered from an erratic block of Campa
nian age in the vicinity of Grodno. In the future this
will serve as a basis for comparison of the material
under consideration with the type material and with
the specimens of these species from other localities. In
addition, the study of bryozoans from the erratic block
in combination with other investigations will allow
more accurate estimates of the age and origin place of
this block. In the colonies of
O. rowei
and
O. mimosa
the piriform and ovate autozooids always budded dis
tally and avicularia budded distolaterally. The vertical
growth of colonies was due to piriform autozooids that
formed vertical rows and the horizontal growth was
due to ovate autozooids and avicularia that formed
horizontal rows. New vertical rows were originated by
avicularia budding from autozooids. From these avic
ularia ovate autozooids were budded distally, from
which in turn piriform autozooids were budded.
It is established that bryozoans of the species
O. rowei
and
O. mimosa
differ in the shape of autozoo
ecial opesia and in the cryptocyst that develops opesi
ular indentations in
O. rowei
and opesiules in
O. mimosa.
Both species are similar in the structure of
avicularia, in which the central part of cryptocyst con
tains an opesium and three opesiules. The colonies of
O. rowei
have yielded reparative avicularia, in addi
tion, some colonies of this species have yielded aber
rant forms.
The intra and intercolonial variability of avicularia
have been studied in
O. rowei
and
O. mimosa.
Three
types of avicularia may be distinguished: type 1 com
prises avicularia with long rostra and long troughlike
apices, type 2 comprises avicularia with short rostra
and short troughlike apices, and type 3 comprises avic
ularia with short rostra without projecting apices. On
this basis the colonies are divided into three groups.
The colonies of the first group are characterized by the
presence of avicularia of type 1 and solitary avicularia
of type 2; in the colonies of the second group avicu
laria of type 2 predominate, but avicularia of type 3
may also be present; in the colonies of the third group
only avicularia of type 3 have been observed. The bry
ozoans of
O. rowei
have yielded all three groups of col
onies, whereas those of
O. mimosa
have only yielded
the second group. In
O. rowei
the colonies of the sec
ond group are most common and avicularia of type 2
predominate in them. Apparently, the emergence of
colonies of the first and third groups, which are char
acterized by the presence of avicularia of types 1 and 3,
reflects possible ways of the formation of new species.
The species
O. rowei
and
O. mimosa
are shown to be
independent and not to belong to the genus
Woodi
pora
. The morphological features largely differentiate
these species from the majority of other species of the
genus
Onychocella
. Obviously, when additional mate
rial will be acquired, the species
O. rowei
and
O. mimosa
may be placed in a separate genus, but this
paper still treats them as members of the genus
Ony
chocella
.
ACKNOWLEDGMENTS
The author is grateful to L.A. Viskova (PIN) for
repeated consultations, to R.A. Rakitov (PIN) for aid
with the scanning electron microscope, and to
V.V. Makhnach (Belarus State University) for provid
ing information on the erratic blocks on the outskirts
of Grodno.
This work was supported by the Russian Foundation
for Basic Research, project no. 140531242mol_a and
no. 130500459a.
Explanation of Plate 10
Figs. 1–6.
Onychocella mimosa
Brydone, 1930: (1) specimen PIN, no. 2922/203: (1a) general appearance of the erect bilateral
colony, (1b, 1c) autozooecia and avicularia, (1d) part of the opesium of autozooecium with a partly destroyed small cryptocystal
tongue, thin white arrow indicates the opesiule, wide white arrow indicates the small tongue; (2) specimen PIN, no. 2922/207:
(2a) general appearance of the erect bilateral colony, (2b) autozooecia and avicularia, (2c) autozooecia with subcircular opesia,
thick black arrows indicate the ooecia, thick white arrow indicates the small tongue, thin black arrow indicates the “suture,” thin
white arrow shows the width of opesium. Scale bars: (1a, 2a) 2 mm; (1b, 1c, 2b) 500
µ
m; (1d, 2c) 200
µ
m.

286
PALEONTOLOGICAL JOURNAL Vol. 48 No. 3 2014
KOROMYSLOVA
REFERENCES
Banta, W.C., The body wall of cheilostome Bryozoa.
II. Interzooidal communication organs,
J. Morphol.
, 1969,
vol. 129, no. 2, pp. 149–170.
Banta, W.C., Gray, N., and Gordon, D.P., A cryptocystal
operculum and new method of lophophore protrusion in
the cheilostome bryozoan
Macropora levinseni
,
Invertebr.
Biol.
, 1997, vol. 116, no. 2, pp. 161–170.
Barskov, I.S. and Weiss, A.F., Microstructure of rostra in the
Upper Cretaceous belemnitellids (Coleoidea, Cepha
lopoda),
Dokl. Akad. Nauk SSSR,
1987, vol. 294, no. 4,
pp. 963–965.
Brydone, R.M., Further notes on the stratigraphy and fauna
of the Trimingham Chalk,
Geol. Mag., New Ser., Dec. V,
1906, vol. 3, no. 7, pp. 289–300.
Brydone, R.M., Notes on new or imperfectly known chalk
Bryozoa (Polyzoa),
Geol. Mag., New Ser., Dec. V
, 1913,
vol. 10, no. 6, pp. 248–250.
Brydone, R.M.,
Further Notes on New or Imperfectly Known
Chalk Polyzoa. Part 2
, London: Dulau and Co., 1930,
pp. 39–60.
Busk, G.,
A monograph of the Fossil Polyzoa of the Crag
,
London: Palaeontogr. Soc., 1859.
Carter, M.C., Gordon, D.P., and Gardner, J.P.A., Polymor
phism and variation in modular animals: Morphometric
and density analyses of bryozoan avicularia,
Mar. Ecol.
Prog. Ser.
, 2010a, vol. 399, pp. 117–130.
Carter, M.C., Gordon, D.P., and Gardner, J.P.A., Polymor
phism and vestigiality: Comparative anatomy and morphol
ogy of bryozoan avicularia,
Zoomorphology
, 2010b, vol. 129,
no. 3, pp. 195–211.
Favorskaya, T.A., Some species of the genus
Onychocella
(Bryozoa, Cheilostomata) from the Maastrichtian of east
ern Turkmenistan and western Uzbekistan,
Ezhegod. Vses.
Paleontol. Obva,
1985, vol. 28, pp. 19–33.
Favorskaya, T.A.,
Prakticheskoe rukovodstvo po makrofaune
Rossii i sopredel’nykh territorii. Mshanki mezokainozoya
(A Practical Handbook on the Macrofauna of Russia and
Adjacent Territories: Bryozoans of the Mesocenozoic),
St. Petersburg: Vses. Geol. Inst., 1996.
Gordon, D.P. and Taylor, P.D., Latest Paleocene to earliest
Eocene bryozoans from Chatham Island, New Zealand,
Bull. Nat. Hist. Mus. London, Geol. Ser.
, 1999, vol. 55, no. 1,
pp. 1–45.
Jebram, D., Preliminary studies on “abnormalities” in bry
ozoans from the point of view of experimental morphology,
Zool. Jahrb. Abt. Anat. Ont. Tiere
, 1978, vol. 100, pp. 245–
275.
Lidgard, S., Zooid and colony growth in encrusting cheilos
tome bryozoans,
Palaeontology
, 1985, vol. 28, no. 2,
pp. 255–291.
Makhnach, A.S., Garetskii, R.G., Matveev, A.V., et al.,
Geologiya Belarusi
(Geology of Belarus), Makhnach, A.S.,
Garetskii, R.G., and Matveev, A.V., Eds., Minsk: Inst.
Geol. Nauk Nats. Akad. Nauk Belarusi, 2001.
McKinney, F.K. and Jackson, J.B.C.,
Bryozoan Evolution,
Spec. Topics Palaeontol. Ser., vol. 2, Boston: Unwin
Hyman, 1989.
Ostrovsky, A.N.,
Evolyutsiya polovogo razmnozheniya msha
nok otryada Cheilostomata (Bryozoa: Gymnolaemata)
(Evo
lution of Sexual Reproduction in the Bryozoan Order
Cheilostomata), St. Petersburg: S.Peterb. Univ., 2009.
Schmidt, R. and Bone, Y., Australian Cenozoic Bryozoa,
1:
Nudicella
gen. nov. (Onychocellidae, Cheilostomata):
taxonomy, palaeoenvironments, and biogeography,
Alcher
inga
, 2004, vol. 28, no. 1, pp. 185–203.
Schubert, T.,
Die Maastrichtstufe in NWDeutschland
,
vol. 8:
Parallele
Merkmalsentwicklung der BryozoenArten
von
Woodipora Jullien 1888 im Coniacium bis Maastrichtium
NWEuropas
, Geol. Jahrb., Reihe A, vol. 98, Stuttgart:
E. Schweizerbart, 1986, pp. 3–83.
Taylor, P.D., Colony growth pattern and astogenetic gradi
ents in the Cretaceous cheilostome bryozoan
Herpetopora
,
Palaeontology
, 1988, vol. 31, no. 2, pp. 519–549.
Taylor, P.D., Late Cretaceous cheilostome bryozoans from
California and Baja California,
J. Paleontol.
, 2008, vol. 82,
no. 4, pp. 823–834.
Taylor, P.D. and Gordon, D.P., Bryozoans from the Late
Cretaceous Kahuitara Tuff of the Chatham Islands,
New Zealand,
Alcheringa
, 2007, vol. 31, no. 4, pp. 339–
363.
Taylor, P.D. and McKinney, F.K., Cretaceous Bryozoa from
the Campanian and Maastrichtian of the Atlantic and Gulf
Coastal Plains, United States,
Scripta Geol.
, 2006, vol. 132,
pp. 1–346.
Viskova, L.A., New finds of Late Cretaceous stenolaema
tous bryozoans with a closed type of growth,
Paleontol. J.,
2000, vol. 34, no. 6, pp. 606–612.
Viskova, L.A., Idmoneiform Tubuliporina (Bryozoa,
Stenolaemata): Morphological features, problems in sys
tematics, and new taxa,
Paleontol. J.
, 2004, vol. 38, no. 1,
pp. 45–59.
Voi g t, E . ,
Oberkreide
Bryozoen aus den asiatischen gebi
eten der UdSSR,
Mitt. Geol. Staatinst. Hamburg
, 1967,
no. 36, pp. 5–95.
Voigt, E., Bryozoen aus dem Campan von Misburg bei
Hannover,
Ber. Naturhist. Ges.
, 1975, vol. 119, pp. 235–277.
Wood, S.V., Descriptive catalogue of the zoophytes from the
Crag,
Ann. Mag. Nat. Hist., Zool., Bot., Geol.
, 1844, vol. 13,
pp. 10–21.
Translated by L. Lukyanov