299
Electra . He also recorded that some eggs were swallowed,
and then defaecated without undergoing any external changes!
The “Membrana vittelina” [fertilization envelope] became
visible and one polar body was recorded soon after release. In
Farrella up to ten ovulated eggs were recorded passing
through the coelomopore. Interestingly, Marcus thought that
the eggs of non-brooding bryozoan species were richer in
yolk than those of brooding forms.
Like Waters and Harmer, Hastings ( 1930 ) remarked on
reproductive structures in her taxonomic papers. For instance,
in the simultaneously hermaphrodite zooids of Bugula uniserialis the ovary is said to be located in funicular tissue just
below the tip of the caecum, and sperm fi lled the proximal
region of the zooid. The ovary of Alderina irregularis was
observed to contain either four small or one large egg, and
sperm and eggs were also found together in the hermaphrodite
zooids of Discoporella umbellata . She described heteromorphic female polypides in Thalamoporella californica that are
considerably smaller than those of other zooids, and suggested
that their only function is that of oviposition. Up to four
embryos are contained in the ovicells. Hastings ( 1932 ) gave
information on reproduction in Stylopoma informata and S.
schizostoma . She followed successive stages of egg development, noting a change in structure of the ovary wall from
“ordinary” to “columnar” [cells] (p. 423) and polypide degeneration and ovicell formation in the latter species. Upon maturation of the fi rst large egg, the polypide degenerates and the
ooecium starts to grow. Egg enlargement continues during
polypide degeneration. Hastings rejected as unsubstantiated
the statement of Canu and Bassler ( 1923 , 1928 ), that the
female polypide “constructed” the ovicell in S . spongites .
Hastings ( 1941 ) recorded simultaneous brooding of up to
seven embryos in ovicells of Scruparia chelata [three embryos
were later recorded in this species by Mawatari ( 1973a )], comparing the species with Thalamoporella and stressing the
“two-valved” appearance of their respective ovicells.
Faulkner ( 1933 ) investigated the early developmental
stages of the polypide in Alcyonidium gelatinosum , accompanied by the formation of a so-called “neoblastic morula”
[early stages of ovary formation]. Sexual zooids were
described as gonochoristic, occurring simultaneously in the
colonies of this species. Prospective germ cells (“neoblasts”)
fi rst appear in the zone of actively dividing cells of the developing polypide bud attached to the cystid wall. In this zone
the epithelial layers of the zooid wall and polypide rudiment
are confl uent. Here, one or two “neoblasts” [presumably primordial germ cells] appear, clearly distinguished from other
cells by their large size, nuclear characteristics, staining and
position. They further migrate distally between the layers of
the bilayered polypide bud to its apex, proliferate, and form a
“cell-colony” or “neoblastic morula” (pp. 257, 263) between
the epithelium of the developing caecum and adjacent
mesothelial lining [future ovary wall] at the confl uence of the
funiculus. According to Faulkner, these totipotential cells
may then either migrate through the basal membrane and participate in the development of the polypide gut (in prospective
sterile zooids) or form an ovary (in the case of female zooids).
Faulkner noted that Silbermann ( 1906 ) saw “neoblasts” but
did not recognize them (for further discussion see Reed
1991 ). A more-advanced stage of ovarian development is
seen when its cells [oocytes] are aligned in a linear series.
Further, each oocyte is surrounded by its own follicle.
Zirpolo ( 1933 ) confi rmed observations of Waters ( 1914 ),
observing brooding in the tentacle sheath of the ctenostome
Zoobotryon verticillatum . In contrast, Braem ( 1940 )
described embryos developing inside a special sac in the
ctenostome Sundanella sibogae (as Victorella ). Judging from
his illustrations, this sac is an invagination of the zooidal
body wall. The structural changes in the sac walls during
brooding, together with the very large increase in embryo
size, implies that he discovered a placental analogue in this
species, in which the polypide degenerates and the mature
embryo occupies most of the zooid cavity. Braem supposed
that the embryo escaped through the narrow distal “neck” of
the incubation sac. Silén ( 1942 , 1944) found similar sacs in
the ctenostome Nolella papuensis , describing its wall as
thick when containing the large embryo and thin when the
embryo is small. It seems that placental brooding is present
in this species also. It should be mentioned that extraembryonic nutrition has recently been confi rmed at the ultrastructural level for Zoobotryon verticillatum (Ostrovsky and
Schwaha 2011 ).
Stach ( 1938 ) studied reproduction in the cheilostome
“ Carbasea ” indivisa . According to his description, colonies
included both male and female zooids, although, occasionally, oocytes and sperm were seen in the same zooid. The
presence of both gonochoristic and hermaphrodite zooids
might be evidence that all sexual zooids are functionally hermaphrodite (see above). The ovary, with 4–7 oocytes, was
found suspended on the funiculus near the proximal transverse and lateral walls. The polypide usually undergoes recycling during oogenesis. Spermatogenic tissue develops on
both lateral and transverse (distal and proximal) walls. Stach
reported that, following fertilization, ovulated oocytes
increase in size and have an “irregular sinuate outline” (p. 395;
see also pl. 1, fi g. 2). The latter illustration also shows the
angular shape of coelomic oocytes. Oviposition was not
observed, but 3–7 released eggs become attached to the
lower surface of the zooidal operculum, each egg being surrounded by a transparent, elongated “brood-sac”. These
chambers are described as developing from the distal portion
of the tentacle sheath [i.e. vestibulum], which forms the
inner wall of the operculum. As depicted in his illustrations,
each sac has a thin stalk, situated close to those of neighbouring sacs. There are some differences in the timing of embryo
development, apparently depending on differences in the
Appendices
Electra . He also recorded that some eggs were swallowed,
and then defaecated without undergoing any external changes!
The “Membrana vittelina” [fertilization envelope] became
visible and one polar body was recorded soon after release. In
Farrella up to ten ovulated eggs were recorded passing
through the coelomopore. Interestingly, Marcus thought that
the eggs of non-brooding bryozoan species were richer in
yolk than those of brooding forms.
Like Waters and Harmer, Hastings ( 1930 ) remarked on
reproductive structures in her taxonomic papers. For instance,
in the simultaneously hermaphrodite zooids of Bugula uniserialis the ovary is said to be located in funicular tissue just
below the tip of the caecum, and sperm fi lled the proximal
region of the zooid. The ovary of Alderina irregularis was
observed to contain either four small or one large egg, and
sperm and eggs were also found together in the hermaphrodite
zooids of Discoporella umbellata . She described heteromorphic female polypides in Thalamoporella californica that are
considerably smaller than those of other zooids, and suggested
that their only function is that of oviposition. Up to four
embryos are contained in the ovicells. Hastings ( 1932 ) gave
information on reproduction in Stylopoma informata and S.
schizostoma . She followed successive stages of egg development, noting a change in structure of the ovary wall from
“ordinary” to “columnar” [cells] (p. 423) and polypide degeneration and ovicell formation in the latter species. Upon maturation of the fi rst large egg, the polypide degenerates and the
ooecium starts to grow. Egg enlargement continues during
polypide degeneration. Hastings rejected as unsubstantiated
the statement of Canu and Bassler ( 1923 , 1928 ), that the
female polypide “constructed” the ovicell in S . spongites .
Hastings ( 1941 ) recorded simultaneous brooding of up to
seven embryos in ovicells of Scruparia chelata [three embryos
were later recorded in this species by Mawatari ( 1973a )], comparing the species with Thalamoporella and stressing the
“two-valved” appearance of their respective ovicells.
Faulkner ( 1933 ) investigated the early developmental
stages of the polypide in Alcyonidium gelatinosum , accompanied by the formation of a so-called “neoblastic morula”
[early stages of ovary formation]. Sexual zooids were
described as gonochoristic, occurring simultaneously in the
colonies of this species. Prospective germ cells (“neoblasts”)
fi rst appear in the zone of actively dividing cells of the developing polypide bud attached to the cystid wall. In this zone
the epithelial layers of the zooid wall and polypide rudiment
are confl uent. Here, one or two “neoblasts” [presumably primordial germ cells] appear, clearly distinguished from other
cells by their large size, nuclear characteristics, staining and
position. They further migrate distally between the layers of
the bilayered polypide bud to its apex, proliferate, and form a
“cell-colony” or “neoblastic morula” (pp. 257, 263) between
the epithelium of the developing caecum and adjacent
mesothelial lining [future ovary wall] at the confl uence of the
funiculus. According to Faulkner, these totipotential cells
may then either migrate through the basal membrane and participate in the development of the polypide gut (in prospective
sterile zooids) or form an ovary (in the case of female zooids).
Faulkner noted that Silbermann ( 1906 ) saw “neoblasts” but
did not recognize them (for further discussion see Reed
1991 ). A more-advanced stage of ovarian development is
seen when its cells [oocytes] are aligned in a linear series.
Further, each oocyte is surrounded by its own follicle.
Zirpolo ( 1933 ) confi rmed observations of Waters ( 1914 ),
observing brooding in the tentacle sheath of the ctenostome
Zoobotryon verticillatum . In contrast, Braem ( 1940 )
described embryos developing inside a special sac in the
ctenostome Sundanella sibogae (as Victorella ). Judging from
his illustrations, this sac is an invagination of the zooidal
body wall. The structural changes in the sac walls during
brooding, together with the very large increase in embryo
size, implies that he discovered a placental analogue in this
species, in which the polypide degenerates and the mature
embryo occupies most of the zooid cavity. Braem supposed
that the embryo escaped through the narrow distal “neck” of
the incubation sac. Silén ( 1942 , 1944) found similar sacs in
the ctenostome Nolella papuensis , describing its wall as
thick when containing the large embryo and thin when the
embryo is small. It seems that placental brooding is present
in this species also. It should be mentioned that extraembryonic nutrition has recently been confi rmed at the ultrastructural level for Zoobotryon verticillatum (Ostrovsky and
Schwaha 2011 ).
Stach ( 1938 ) studied reproduction in the cheilostome
“ Carbasea ” indivisa . According to his description, colonies
included both male and female zooids, although, occasionally, oocytes and sperm were seen in the same zooid. The
presence of both gonochoristic and hermaphrodite zooids
might be evidence that all sexual zooids are functionally hermaphrodite (see above). The ovary, with 4–7 oocytes, was
found suspended on the funiculus near the proximal transverse and lateral walls. The polypide usually undergoes recycling during oogenesis. Spermatogenic tissue develops on
both lateral and transverse (distal and proximal) walls. Stach
reported that, following fertilization, ovulated oocytes
increase in size and have an “irregular sinuate outline” (p. 395;
see also pl. 1, fi g. 2). The latter illustration also shows the
angular shape of coelomic oocytes. Oviposition was not
observed, but 3–7 released eggs become attached to the
lower surface of the zooidal operculum, each egg being surrounded by a transparent, elongated “brood-sac”. These
chambers are described as developing from the distal portion
of the tentacle sheath [i.e. vestibulum], which forms the
inner wall of the operculum. As depicted in his illustrations,
each sac has a thin stalk, situated close to those of neighbouring sacs. There are some differences in the timing of embryo
development, apparently depending on differences in the
Appendices