45
ovary, in which an oocyte doublet was located, comprises
fl atter cells. A prominent intraovarian zone is represented by
an aggregate of paler basal cells of irregular shape; in histological sections it looks like a rupture of the lower ovary
wall, with peripheral basal cells overlying the cystid epithelium. All ovaries seen in this species contained a single
oocyte doublet, consisting of a small macrolecithal oocyte
and its nurse cell.
In addition to the above-mentioned species, pattern IV has
been found in Klugefl ustra antarctica and Isosecurifl ustra
angusta (Flustridae), Micropora notialis (Microporidae),
Figularia fi gularis (Cribrilinidae), Cribricellina cribraria
(Catenicellidae), “Calyptotheca” variolosa (Lanceoporidae),
Watersipora subtorquata (Watersiporidae), Myriapora truncata (Myriaporidae), and provisionally Scrupocellaria scruposa (Candidae) (Ostrovsky 2013 ). Note that Isosecurifl ustra
tenuis was found to possess reproductive pattern II and
Cellaria fi stulosa had reproductive pattern III (see above, and
Ostrovsky et al. 2009a ). These fi ndings, as well as the varied
structure of the ovary within this group, indicate the intermediate position of reproductive pattern IV (see Sect. 3.3 ).
The number of intra-ovarian oocyte doublets varies from
two to four; Scrupocellaria scruposa is exceptional with up
to six doublets. Isosecurifl ustra angusta sometimes had two
vitellogenic doublets developing simultaneously in the ovary
(similar to some species with reproductive pattern II).
Oocyte size at the beginning of vitellogenesis was measured as 47 × 37 μm (nurse cell 36 × 35 μm) in Beania bilaminata , 50 μm in Micropora notialis (no data for early nurse
cells), 56 × 52.5 μm (nurse cell 26 × 21 μm) in Cellaria tenuirostris and 85 μm (nurse cell 70 × 55 μm) in “Calyptotheca”
variolosa (see Tables 1.4 and 1.5 ).
Mature (about to ovulate or ovulated) oocytes are macrolecithal (Figs. 1.29A and 1.33D, F ), whether small or large.
Minimum oocyte size occurred in B. bilaminata
(55.2 × 50.4 μm) and C. tenuirostris (85 × 58 μm) with a maximum of 335 μm in Cribricellina cribraria . In B. bilaminata
and Myriapora truncata , yolk granules were found not only
in oocytes but also in nurse cells.
The degree of enlargement of the oocyte during intraovarian development in species with reproductive pattern
IV is similar to that in species with reproductive pattern II.
Oocyte volume increases by two or three orders of magnitude while in the ovary and 2.2–17-fold during vitellogenesis. Maximum embryonic enlargement during brooding
was found in B. bilaminata (468.2-fold) with a minimum of
1.27- fold and 1.49-fold in Isosecurifl ustra angusta and
Figularia fi gularis , respectively. In the embryo cells of all
the matrotrophic bryozoans studied, yolk granules increase
in size, changing their shape and sometimes their staining
intensity.
In “Calyptotheca” variolosa , the cytoplasm of many
ovary-wall cells, including fl at follicle cells, contained tiny
dark granules that stain more intensely than do yolk granules
in the oocyte (Fig. 1.33F ). Flat follicle cells in the ovaries
with an early vitellogenic doublet have no granules at this
stage.
1.2.6.3 Embryophore
In general, the structure of the embryophore in species with
reproductive pattern IV is similar to that in species with pattern III (Ostrovsky 2013 ). Both Klugefl ustra antarctica and
Isosecurifl ustra angusta have a small ooecial vesicle and the
embryophore consists of relatively few large columnar epithelial cells associated with funicular cords (Fig. 1.31 ).
These cells have pale cytoplasm and large nuclei, and are
considerably larger than most of the other somatic cells.
A small ooecial vesicle plugs the entrance to the hyperstomial ovicell in Micropora notialis . During incubation, its
epithelial cells enlarge and the cytoplasm stains intensely. It
is possible that the number of epithelial and funicular cells
increase within the embryophore since they fi ll most of the
ooecial vesicle in the manner of loose “parenchyma”
(Fig. 1.28B ).
The endozooidal ovicells of Figularia fi gularis lack an
ooecial vesicle, the distal wall of the maternal zooid taking
over this role. The lower half of the wall has a thin cuticle,
and a relatively small embryophore is formed there during
incubation (Fig. 1.28A ). It comprises large columnar cells
with fi ne-grained, deeply staining cytoplasm and associated
funicular cells.
In Cellaria tenuirostris , the structure of the embryophore
in the endotoichal ovicell is identical to that in C . fi stulosa
with pattern III (see Fig. 1.19B–D ). Embryophore cells show
a moderate increase in size during embryo development,
transforming from fl at to oval with intensely staining
cytoplasm (Fig. 1.29b ). Moderate enlargement is also characteristic of embryophore cells in the hyperstomial ovicells
of Cribricellina cribraria (in which a dense network of the
thin funicular cords develops) (Fig. 1.32 ) and the internal
brood sac of Watersipora subtorquata (Fig. 2.47B ). In the
latter, large cells were often found either on zooid walls or in
the zooid cavity associated with funicular cords. They were
often grouped (Fig. 1.14A ) and are presumed to be for nutrient storage.
In Beania bilaminata (Fig. 1.22 ), matrotrophic incubation occurs in the brood sac that is immersed in the distal
part of the maternal zooid and communicates with the external medium via a narrow “neck,” as in Watersipora subtorquata . The wall of the sac is serviced by numerous funicular
cords and consists of a thin cuticle and an embryophore of
large cubic epithelial cells (with pale cytoplasm and oval
nucleus) associated with a few fl at funicular cells. In sacs
with early and mid-stage embryos, numerous dark granules
are found in the apical (facing the embryo) part of the
epithelial cells of the embryophore. Their cytoplasm also
1.2 Reproductive Patterns of Bryozoa
ovary, in which an oocyte doublet was located, comprises
fl atter cells. A prominent intraovarian zone is represented by
an aggregate of paler basal cells of irregular shape; in histological sections it looks like a rupture of the lower ovary
wall, with peripheral basal cells overlying the cystid epithelium. All ovaries seen in this species contained a single
oocyte doublet, consisting of a small macrolecithal oocyte
and its nurse cell.
In addition to the above-mentioned species, pattern IV has
been found in Klugefl ustra antarctica and Isosecurifl ustra
angusta (Flustridae), Micropora notialis (Microporidae),
Figularia fi gularis (Cribrilinidae), Cribricellina cribraria
(Catenicellidae), “Calyptotheca” variolosa (Lanceoporidae),
Watersipora subtorquata (Watersiporidae), Myriapora truncata (Myriaporidae), and provisionally Scrupocellaria scruposa (Candidae) (Ostrovsky 2013 ). Note that Isosecurifl ustra
tenuis was found to possess reproductive pattern II and
Cellaria fi stulosa had reproductive pattern III (see above, and
Ostrovsky et al. 2009a ). These fi ndings, as well as the varied
structure of the ovary within this group, indicate the intermediate position of reproductive pattern IV (see Sect. 3.3 ).
The number of intra-ovarian oocyte doublets varies from
two to four; Scrupocellaria scruposa is exceptional with up
to six doublets. Isosecurifl ustra angusta sometimes had two
vitellogenic doublets developing simultaneously in the ovary
(similar to some species with reproductive pattern II).
Oocyte size at the beginning of vitellogenesis was measured as 47 × 37 μm (nurse cell 36 × 35 μm) in Beania bilaminata , 50 μm in Micropora notialis (no data for early nurse
cells), 56 × 52.5 μm (nurse cell 26 × 21 μm) in Cellaria tenuirostris and 85 μm (nurse cell 70 × 55 μm) in “Calyptotheca”
variolosa (see Tables 1.4 and 1.5 ).
Mature (about to ovulate or ovulated) oocytes are macrolecithal (Figs. 1.29A and 1.33D, F ), whether small or large.
Minimum oocyte size occurred in B. bilaminata
(55.2 × 50.4 μm) and C. tenuirostris (85 × 58 μm) with a maximum of 335 μm in Cribricellina cribraria . In B. bilaminata
and Myriapora truncata , yolk granules were found not only
in oocytes but also in nurse cells.
The degree of enlargement of the oocyte during intraovarian development in species with reproductive pattern
IV is similar to that in species with reproductive pattern II.
Oocyte volume increases by two or three orders of magnitude while in the ovary and 2.2–17-fold during vitellogenesis. Maximum embryonic enlargement during brooding
was found in B. bilaminata (468.2-fold) with a minimum of
1.27- fold and 1.49-fold in Isosecurifl ustra angusta and
Figularia fi gularis , respectively. In the embryo cells of all
the matrotrophic bryozoans studied, yolk granules increase
in size, changing their shape and sometimes their staining
intensity.
In “Calyptotheca” variolosa , the cytoplasm of many
ovary-wall cells, including fl at follicle cells, contained tiny
dark granules that stain more intensely than do yolk granules
in the oocyte (Fig. 1.33F ). Flat follicle cells in the ovaries
with an early vitellogenic doublet have no granules at this
stage.
1.2.6.3 Embryophore
In general, the structure of the embryophore in species with
reproductive pattern IV is similar to that in species with pattern III (Ostrovsky 2013 ). Both Klugefl ustra antarctica and
Isosecurifl ustra angusta have a small ooecial vesicle and the
embryophore consists of relatively few large columnar epithelial cells associated with funicular cords (Fig. 1.31 ).
These cells have pale cytoplasm and large nuclei, and are
considerably larger than most of the other somatic cells.
A small ooecial vesicle plugs the entrance to the hyperstomial ovicell in Micropora notialis . During incubation, its
epithelial cells enlarge and the cytoplasm stains intensely. It
is possible that the number of epithelial and funicular cells
increase within the embryophore since they fi ll most of the
ooecial vesicle in the manner of loose “parenchyma”
(Fig. 1.28B ).
The endozooidal ovicells of Figularia fi gularis lack an
ooecial vesicle, the distal wall of the maternal zooid taking
over this role. The lower half of the wall has a thin cuticle,
and a relatively small embryophore is formed there during
incubation (Fig. 1.28A ). It comprises large columnar cells
with fi ne-grained, deeply staining cytoplasm and associated
funicular cells.
In Cellaria tenuirostris , the structure of the embryophore
in the endotoichal ovicell is identical to that in C . fi stulosa
with pattern III (see Fig. 1.19B–D ). Embryophore cells show
a moderate increase in size during embryo development,
transforming from fl at to oval with intensely staining
cytoplasm (Fig. 1.29b ). Moderate enlargement is also characteristic of embryophore cells in the hyperstomial ovicells
of Cribricellina cribraria (in which a dense network of the
thin funicular cords develops) (Fig. 1.32 ) and the internal
brood sac of Watersipora subtorquata (Fig. 2.47B ). In the
latter, large cells were often found either on zooid walls or in
the zooid cavity associated with funicular cords. They were
often grouped (Fig. 1.14A ) and are presumed to be for nutrient storage.
In Beania bilaminata (Fig. 1.22 ), matrotrophic incubation occurs in the brood sac that is immersed in the distal
part of the maternal zooid and communicates with the external medium via a narrow “neck,” as in Watersipora subtorquata . The wall of the sac is serviced by numerous funicular
cords and consists of a thin cuticle and an embryophore of
large cubic epithelial cells (with pale cytoplasm and oval
nucleus) associated with a few fl at funicular cells. In sacs
with early and mid-stage embryos, numerous dark granules
are found in the apical (facing the embryo) part of the
epithelial cells of the embryophore. Their cytoplasm also
1.2 Reproductive Patterns of Bryozoa