39
(Fig. 1.13A ) and Cribrilina annulata (Fig. 1.10E ) (see
Wourms ( 1987 ) for defi nitions and discussion). In the latter
species, both plasmalecithal and telolecithal oocytes were
recorded.
In comparing the diameter of mature oocytes, several size
groups were distinguished among the species studied. In four
species belonging to different families (Bugulidae, Flustridae,
Candidae, Microporellidae), mature oocytes were less than
90 μm diameter (ranging from 68 μm in Dendrobeania fruticosa to 87.5 μm in Microporella ciliata ). Provisional size
classes of mature oocytes yield diameters of 102.5 μm to
147.5 μm in 27 species, 159.5–187.5 μm in 18 species and
217.5–275.0 μm in seven species. In a few other species, the
size of mature oocytes exceeded 300 μm: 305 μm in
Steginocellaria magnimandibulata (Cellariidae), 320 μm in
Petralia undata (Petraliidae)), and 402.5 μm in Melicerita
obliqua (Cellariidae). The ten species with the largest
oocytes belonged to ten different families. Extreme size
groups can occur in the same family – for instance, among
fl ustrids the smallest oocytes encountered were 70 μm (in
Gregarinidra inarmata ) and the largest 220 μm (in
Isosecurifl ustra tenuis ). Dendrobeania fruticosa (68 μm) and
Cornucopina polymorpha (181.25 μm) constituted extremes
among bugulids (see Table 1.6 ).
Mature oocytes are normally oval or elliptical but, depending on spatial limitations in the cystid, they can be angular
( Steginocellaria magnimandibulata ) or occasionally lobate
as in Sinuporaria sp. (Lepraliellidae) and Smittina concinna
(Smittinidae). Lobate oocytes were in fact depicted by
Repiachoff ( 1876 ) in the ovary of non-brooding Electra
repiachowi (Electridae).
In most cases the cytoplasm of mature macrolecithal
oocytes contains numerous darkly staining, rounded or oval
yolk granules of different size (Figs. 1.10C–F , 1.11A–C ,
1.12C, D , 1.13A, B, D , 1.14C, D , 1.15 and 1.30A ). In contrast, the oocyte cytoplasm in Securifl ustra securifrons
(Flustridae) (Fig. 1.11D ) was fi lled with tiny pale vacuoles or
granules, whose borders were discernible only at high magnifi cation. At low magnifi cation the cells appeared to have an
evenly stained pale matrix with few or no inclusions. Apart
from these, non-staining vacuoles were sometimes seen.
They were usually small, but sometimes attained 15 μm
diameter. These vacuoles were never more numerous than
3–4 and always situated at the vegetal pole of the cell bordering the intraovarian space (possibly indicative of a site of
nutrient transport). Large pale vacuoles (sometimes almost
as large as the nucleus or larger) were found in the cytoplasm
of all oocyte doublets in the ovaries of Quadriscutella papillata (Fig. 1.14C ). They were considerably smaller in mature
oocytes than in immature ones.
The nuclei of oocytes are usually oval or, sometimes,
round (Figs. 1.10D , 1.12C , 1.13A , 1.14C and 1.15C ). In
some cases ( Securifl ustra securifrons , Dimetopia cornuta )
the nucleus may be irregular, even lobate (Fig. 1.11D ). A
folded nuclear envelope was also noted in the calloporid
Cauloramphus spinifer (Fig. 1.8C ). With the exception of
Exochella sp., nuclei and nucleoli of mature oocytes and
nurse cells were larger than those of early vitellogenic
oocytes. The diameter of the oocyte nucleus at the beginning of the yolk-accumulation phase varied from 13 μm
(several species) to 45 μm ( Steginoporella perplexa ). The
diameter of nucleoli varied from 3 μm to 12.5 μm. At the
end of vitellogenesis the size of the oocyte nucleus ranged
from 18.5 × 11.25 μm ( Corbulella maderensis ) to 83 μm
( Petralia undata ). The diameter of nucleoli in mature
oocytes varied from 5 μm ( Sinuporaria sp.) to 22 μm
(“ Bifl ustra ” perfragilis ). In 11 species the nuclei of mature
oocytes contained more than one (2–7) nucleoli, undoubtedly indicating active synthesis in the growing cell (see
Table 1.6 ).
The nuclear envelope of the oocyte almost always collapses prior to ovulation, i.e. while the female cell is still in
the ovary. Nevertheless, in Arachnopusia unicornis a mature
primary oocyte with a nucleus containing clearly discernible
chromosomes was seen in an ovicell. Thus, the breakdown of
the germinal vesicle may be delayed.
In early and mid-stage vitellogenic doublets some of the
surface of the nurse cell (as well as that of its oocyte sibling)
is exposed to the intraovarian zone. In mature ovaries this
contact is often not very evident, the nurse cell being
squeezed between the large oocyte and the follicle wall
(Figs. 1.10C and 1.11A ), almost always in the lower part of
the ovary. Nurse cells in the fi nal stage of oocyte-doublet
development are, as a rule, larger than those that have just
started vitellogenesis. In only three of the species studied
( Cribrilina annulata , Porella minuta , Turbicellepora avicularis ) the diameter of nurse cells was more or less the same
throughout vitellogenesis.
Nurse-cell nuclei and nucleoli increase in size during
maturation, similar to the situation in oocytes. The minimum diameter of nurse-cell nuclei at the onset of vitellogenesis was found to be 11 μm in Dimetopia cornuta and
maximally 51 × 33 μm in Margaretta barbata , respectively
slightly less than the diameter of the nucleus in their sibling
oocytes. Nucleolus diameter varied from 4.5 μm to
14 × 13 μm. The minimum diameter of nurse-cell nuclei at
the end of vitellogenesis was 14 μm in Gregarinidra inarmata and Dimetopia cornuta and maximally 60 × 55 μm in
Melicerita obliqua , much smaller than the diameter of
nuclei in mature sibling oocytes. The diameter of nucleoli in
mature nurse cells varied from 5–6 μm to 20 μm (see
Tables 1.5 and 1.7 ).
In 28 species (including calloporids) yolk granules were
found not only in oocytes but also in nurse cells (Fig. 1.8D ,
inset), ranging from few to numerous. In early vitellogenic
doublets of Bostrichopora dentata (Smittinidae) yolk granules
1.2 Reproductive Patterns of Bryozoa
(Fig. 1.13A ) and Cribrilina annulata (Fig. 1.10E ) (see
Wourms ( 1987 ) for defi nitions and discussion). In the latter
species, both plasmalecithal and telolecithal oocytes were
recorded.
In comparing the diameter of mature oocytes, several size
groups were distinguished among the species studied. In four
species belonging to different families (Bugulidae, Flustridae,
Candidae, Microporellidae), mature oocytes were less than
90 μm diameter (ranging from 68 μm in Dendrobeania fruticosa to 87.5 μm in Microporella ciliata ). Provisional size
classes of mature oocytes yield diameters of 102.5 μm to
147.5 μm in 27 species, 159.5–187.5 μm in 18 species and
217.5–275.0 μm in seven species. In a few other species, the
size of mature oocytes exceeded 300 μm: 305 μm in
Steginocellaria magnimandibulata (Cellariidae), 320 μm in
Petralia undata (Petraliidae)), and 402.5 μm in Melicerita
obliqua (Cellariidae). The ten species with the largest
oocytes belonged to ten different families. Extreme size
groups can occur in the same family – for instance, among
fl ustrids the smallest oocytes encountered were 70 μm (in
Gregarinidra inarmata ) and the largest 220 μm (in
Isosecurifl ustra tenuis ). Dendrobeania fruticosa (68 μm) and
Cornucopina polymorpha (181.25 μm) constituted extremes
among bugulids (see Table 1.6 ).
Mature oocytes are normally oval or elliptical but, depending on spatial limitations in the cystid, they can be angular
( Steginocellaria magnimandibulata ) or occasionally lobate
as in Sinuporaria sp. (Lepraliellidae) and Smittina concinna
(Smittinidae). Lobate oocytes were in fact depicted by
Repiachoff ( 1876 ) in the ovary of non-brooding Electra
repiachowi (Electridae).
In most cases the cytoplasm of mature macrolecithal
oocytes contains numerous darkly staining, rounded or oval
yolk granules of different size (Figs. 1.10C–F , 1.11A–C ,
1.12C, D , 1.13A, B, D , 1.14C, D , 1.15 and 1.30A ). In contrast, the oocyte cytoplasm in Securifl ustra securifrons
(Flustridae) (Fig. 1.11D ) was fi lled with tiny pale vacuoles or
granules, whose borders were discernible only at high magnifi cation. At low magnifi cation the cells appeared to have an
evenly stained pale matrix with few or no inclusions. Apart
from these, non-staining vacuoles were sometimes seen.
They were usually small, but sometimes attained 15 μm
diameter. These vacuoles were never more numerous than
3–4 and always situated at the vegetal pole of the cell bordering the intraovarian space (possibly indicative of a site of
nutrient transport). Large pale vacuoles (sometimes almost
as large as the nucleus or larger) were found in the cytoplasm
of all oocyte doublets in the ovaries of Quadriscutella papillata (Fig. 1.14C ). They were considerably smaller in mature
oocytes than in immature ones.
The nuclei of oocytes are usually oval or, sometimes,
round (Figs. 1.10D , 1.12C , 1.13A , 1.14C and 1.15C ). In
some cases ( Securifl ustra securifrons , Dimetopia cornuta )
the nucleus may be irregular, even lobate (Fig. 1.11D ). A
folded nuclear envelope was also noted in the calloporid
Cauloramphus spinifer (Fig. 1.8C ). With the exception of
Exochella sp., nuclei and nucleoli of mature oocytes and
nurse cells were larger than those of early vitellogenic
oocytes. The diameter of the oocyte nucleus at the beginning of the yolk-accumulation phase varied from 13 μm
(several species) to 45 μm ( Steginoporella perplexa ). The
diameter of nucleoli varied from 3 μm to 12.5 μm. At the
end of vitellogenesis the size of the oocyte nucleus ranged
from 18.5 × 11.25 μm ( Corbulella maderensis ) to 83 μm
( Petralia undata ). The diameter of nucleoli in mature
oocytes varied from 5 μm ( Sinuporaria sp.) to 22 μm
(“ Bifl ustra ” perfragilis ). In 11 species the nuclei of mature
oocytes contained more than one (2–7) nucleoli, undoubtedly indicating active synthesis in the growing cell (see
Table 1.6 ).
The nuclear envelope of the oocyte almost always collapses prior to ovulation, i.e. while the female cell is still in
the ovary. Nevertheless, in Arachnopusia unicornis a mature
primary oocyte with a nucleus containing clearly discernible
chromosomes was seen in an ovicell. Thus, the breakdown of
the germinal vesicle may be delayed.
In early and mid-stage vitellogenic doublets some of the
surface of the nurse cell (as well as that of its oocyte sibling)
is exposed to the intraovarian zone. In mature ovaries this
contact is often not very evident, the nurse cell being
squeezed between the large oocyte and the follicle wall
(Figs. 1.10C and 1.11A ), almost always in the lower part of
the ovary. Nurse cells in the fi nal stage of oocyte-doublet
development are, as a rule, larger than those that have just
started vitellogenesis. In only three of the species studied
( Cribrilina annulata , Porella minuta , Turbicellepora avicularis ) the diameter of nurse cells was more or less the same
throughout vitellogenesis.
Nurse-cell nuclei and nucleoli increase in size during
maturation, similar to the situation in oocytes. The minimum diameter of nurse-cell nuclei at the onset of vitellogenesis was found to be 11 μm in Dimetopia cornuta and
maximally 51 × 33 μm in Margaretta barbata , respectively
slightly less than the diameter of the nucleus in their sibling
oocytes. Nucleolus diameter varied from 4.5 μm to
14 × 13 μm. The minimum diameter of nurse-cell nuclei at
the end of vitellogenesis was 14 μm in Gregarinidra inarmata and Dimetopia cornuta and maximally 60 × 55 μm in
Melicerita obliqua , much smaller than the diameter of
nuclei in mature sibling oocytes. The diameter of nucleoli in
mature nurse cells varied from 5–6 μm to 20 μm (see
Tables 1.5 and 1.7 ).
In 28 species (including calloporids) yolk granules were
found not only in oocytes but also in nurse cells (Fig. 1.8D ,
inset), ranging from few to numerous. In early vitellogenic
doublets of Bostrichopora dentata (Smittinidae) yolk granules
1.2 Reproductive Patterns of Bryozoa