309
In contrast, larval release may occur without a polypide
since the musculature and innervation of the ooecial vesicle are part of the cystid. Ovaries regress in winter when
polypides fail to regenerate in the female zooids, sex reversal taking place the following spring with spermatogenic
tissue developing in many. The authors suggested that in
normal female zooids the ovary produces a factor that suppresses male cells, thus female autozooids may not be
gonochoristic after all.
In Bugula fl abellata mature sperm and an egg that develops into a larva are produced by each polypide generation,
including the fi rst, in hermaphrodite autozooids. Protogyny
prevails; the egg matures more or less half way through the
life of the polypide, whereas sperm mature just before the
polypide degenerates. The ovary is situated on the basal wall
in the proximal part of the zooid, with spermatogenic tissue
on the lateral and proximal transverse walls. Oocytes grow
in pairs [oocyte doublets]. The ovicell completes its formation as the fi rst egg ovulates, both events occurring halfway
through the life of the fi rst polypide. Following oviposition,
the egg receives extraembryonic nutrition via a placenta,
thereafter increasing about 6.5 times in volume, much less
than in B . neritina as described by Woollacott and Zimmer
( 1975 ). Embryogenesis continues through the rest of the
fi rst polypide cycle and into the second, with larval release
taking place when the new polypide starts to feed and prior
to ovulation of the next egg. The authors suggested that the
evolution of placental brooding provides uninterrupted
extraembryonic nutrition throughout polypide cycling by
“spreading the nutrient demands” over two polypide generations (Dyrynda and Ryland 1982 , p. 255). Whilst there is no
feeding polypide in the fertile zooid, extraembryonic
nutrition can be provided from the degenerated-polypide
resouces accumulated in “peritoneal nutrient storage cells”.
According to their suggestion, all this corresponds with the
need to maximise larval productivity in species with ephemeral colonies.
The above research was aided by a light- and TEMmicroscopic study of spermato- and oogenesis (Dyrynda and
King 1983 ). In Chartella papyracea the initial cluster of
female germ cells is established in the maternal coelom on
funicular cords but later migrates to the lateral wall. The
enlarged oogonium divides into an oocyte-nurse-cell doublet, the cells of which are identical in structure and connected by an intercellular bridge. Each doublet is enclosed
by follicle cells that have no peritoneal covering. Dyrynda
and King described oogenesis in detail and made measurements, showing a 175-fold enlargement of the oocyte during
vitellogenesis. During early and middle vitellogenesis, yolk
platelets (described as autosynthesized yolk) appear throughout the oocyte cytoplasm, the oolemma forms numerous
microvilli with pinocytotic vesicles (described as a source of
heterosynthesized yolk) between their bases and the vitelline
envelope begins to form. Pinocytosis ceases during the middle vitellogenic stage, microvilli are withdrawn, and the
“vitelline coat” differentiates into two layers prior to maturation.
The nurse cell also performs pinocytosis between its microvilli and has a vitelline envelope. It produces ribosomes that
are transported to the sibling via the cytoplasmic bridge. It
additionally forms protein platelets but there is no evidence
of their transport. The follicle epithelium is described as differentiating into two layers of squamous (inner) and columnar (outer) cells, the latter performing the synthetic activity.
Sperm heads were recorded in both pre- and vitellogenic
oocytes. Cytokinesis occurs during ovulation, after which
the nurse cell and follicle cells degrade. The mature telolecithal oocyte contains numerous protein platelets and lipid
inclusions. Prior to transfer to the ovicell, it envelops the terminal parts of the gut and is constricted to a diameter of
approximately 10 μm (from 140 μm) during its passage
through the supraneural pore. Brooding is non-placental, so
the embryo is of the same size as the mature egg. The ovarian
cycle is similar in Bugula fl abellata and oocytes develop in
doublets that are connected by the cytoplasmic bridge and a
series of plate desmosomes. Both cells of a pair are surrounded by a vitelline envelope, form microvilli and perform
pinocytosis. The nurse cell produces a few protein platelets
and numerous ribonucleoproteins, being characterized by a
large convoluted nucleus (similar to that described for
Chartella ). The number of ovarian cells is much less in
Bugula . Notably, there is also a striking difference between
the fl ustrid Chartella membranaceotruncata and the bugulid
Bugula calathus in the number of ovary cells, as fi rst recorded
by Vigelius ( 1886 ). Both auto- and heterosynthesized sources
of yolk are suggested. Egg volume increases about 29-fold
during vitellogenesis, and embryo volume enlarges by about
seven times during placental brooding. Nutrient storage cells
were discovered, being associated with the peritoneum,
funicular cords and gonads. It should be noted that the mature
egg is described as telolecithal in B . fl abellata , as shown in
the fi gures. Reed ( 1991 ) termed eggs of this species “small
mesolecithal”.
Additionally, Dyrynda and King checked 28 cheilostome
species, recording embryo enlargement only in bugulids
( Bugula and Bicellariella ). In contrast with Bugula neritina ,
in which the embryo grows about 500 times larger (Woollacott
and Zimmer 1975 ), the increase factor varied between 7.1
and 32.7 in other species; in general, the larger the egg the
lesser the nutrient input during the embryonic stage.
In his unpublished Ph.D. dissertation, Hageman ( 1983 )
described the ultrastructure of the ovary and oogenesis in
Membranipora serrilamella . In this malacostegan species
spermatogenic tissue develops as diffuse clusters of spermatogonia from the coelomic peritoneum on the lateral and basal
walls in protandrously hermaphrodite zooids. Earlier, Mawatari
and Mawatari ( 1975 ) reported that the spermatogonia develop
Appendices
In contrast, larval release may occur without a polypide
since the musculature and innervation of the ooecial vesicle are part of the cystid. Ovaries regress in winter when
polypides fail to regenerate in the female zooids, sex reversal taking place the following spring with spermatogenic
tissue developing in many. The authors suggested that in
normal female zooids the ovary produces a factor that suppresses male cells, thus female autozooids may not be
gonochoristic after all.
In Bugula fl abellata mature sperm and an egg that develops into a larva are produced by each polypide generation,
including the fi rst, in hermaphrodite autozooids. Protogyny
prevails; the egg matures more or less half way through the
life of the polypide, whereas sperm mature just before the
polypide degenerates. The ovary is situated on the basal wall
in the proximal part of the zooid, with spermatogenic tissue
on the lateral and proximal transverse walls. Oocytes grow
in pairs [oocyte doublets]. The ovicell completes its formation as the fi rst egg ovulates, both events occurring halfway
through the life of the fi rst polypide. Following oviposition,
the egg receives extraembryonic nutrition via a placenta,
thereafter increasing about 6.5 times in volume, much less
than in B . neritina as described by Woollacott and Zimmer
( 1975 ). Embryogenesis continues through the rest of the
fi rst polypide cycle and into the second, with larval release
taking place when the new polypide starts to feed and prior
to ovulation of the next egg. The authors suggested that the
evolution of placental brooding provides uninterrupted
extraembryonic nutrition throughout polypide cycling by
“spreading the nutrient demands” over two polypide generations (Dyrynda and Ryland 1982 , p. 255). Whilst there is no
feeding polypide in the fertile zooid, extraembryonic
nutrition can be provided from the degenerated-polypide
resouces accumulated in “peritoneal nutrient storage cells”.
According to their suggestion, all this corresponds with the
need to maximise larval productivity in species with ephemeral colonies.
The above research was aided by a light- and TEMmicroscopic study of spermato- and oogenesis (Dyrynda and
King 1983 ). In Chartella papyracea the initial cluster of
female germ cells is established in the maternal coelom on
funicular cords but later migrates to the lateral wall. The
enlarged oogonium divides into an oocyte-nurse-cell doublet, the cells of which are identical in structure and connected by an intercellular bridge. Each doublet is enclosed
by follicle cells that have no peritoneal covering. Dyrynda
and King described oogenesis in detail and made measurements, showing a 175-fold enlargement of the oocyte during
vitellogenesis. During early and middle vitellogenesis, yolk
platelets (described as autosynthesized yolk) appear throughout the oocyte cytoplasm, the oolemma forms numerous
microvilli with pinocytotic vesicles (described as a source of
heterosynthesized yolk) between their bases and the vitelline
envelope begins to form. Pinocytosis ceases during the middle vitellogenic stage, microvilli are withdrawn, and the
“vitelline coat” differentiates into two layers prior to maturation.
The nurse cell also performs pinocytosis between its microvilli and has a vitelline envelope. It produces ribosomes that
are transported to the sibling via the cytoplasmic bridge. It
additionally forms protein platelets but there is no evidence
of their transport. The follicle epithelium is described as differentiating into two layers of squamous (inner) and columnar (outer) cells, the latter performing the synthetic activity.
Sperm heads were recorded in both pre- and vitellogenic
oocytes. Cytokinesis occurs during ovulation, after which
the nurse cell and follicle cells degrade. The mature telolecithal oocyte contains numerous protein platelets and lipid
inclusions. Prior to transfer to the ovicell, it envelops the terminal parts of the gut and is constricted to a diameter of
approximately 10 μm (from 140 μm) during its passage
through the supraneural pore. Brooding is non-placental, so
the embryo is of the same size as the mature egg. The ovarian
cycle is similar in Bugula fl abellata and oocytes develop in
doublets that are connected by the cytoplasmic bridge and a
series of plate desmosomes. Both cells of a pair are surrounded by a vitelline envelope, form microvilli and perform
pinocytosis. The nurse cell produces a few protein platelets
and numerous ribonucleoproteins, being characterized by a
large convoluted nucleus (similar to that described for
Chartella ). The number of ovarian cells is much less in
Bugula . Notably, there is also a striking difference between
the fl ustrid Chartella membranaceotruncata and the bugulid
Bugula calathus in the number of ovary cells, as fi rst recorded
by Vigelius ( 1886 ). Both auto- and heterosynthesized sources
of yolk are suggested. Egg volume increases about 29-fold
during vitellogenesis, and embryo volume enlarges by about
seven times during placental brooding. Nutrient storage cells
were discovered, being associated with the peritoneum,
funicular cords and gonads. It should be noted that the mature
egg is described as telolecithal in B . fl abellata , as shown in
the fi gures. Reed ( 1991 ) termed eggs of this species “small
mesolecithal”.
Additionally, Dyrynda and King checked 28 cheilostome
species, recording embryo enlargement only in bugulids
( Bugula and Bicellariella ). In contrast with Bugula neritina ,
in which the embryo grows about 500 times larger (Woollacott
and Zimmer 1975 ), the increase factor varied between 7.1
and 32.7 in other species; in general, the larger the egg the
lesser the nutrient input during the embryonic stage.
In his unpublished Ph.D. dissertation, Hageman ( 1983 )
described the ultrastructure of the ovary and oogenesis in
Membranipora serrilamella . In this malacostegan species
spermatogenic tissue develops as diffuse clusters of spermatogonia from the coelomic peritoneum on the lateral and basal
walls in protandrously hermaphrodite zooids. Earlier, Mawatari
and Mawatari ( 1975 ) reported that the spermatogonia develop
Appendices