311
Following oviposition, the embryo increases in volume 15.6
times, receiving extraembryonic nutrition in the ovicell.
Initially it is not in contact with the distal wall of the
maternal zooid, which consists of hypertrophied embryophore epithelium covered with a two- layered cuticle. Despite
this barrier, soluble nutrients are obviously released to the
fl uid in the brooding space, where they are taken up by the
embryo. There is no evidence of pinocytosis in the early
embryo surrounded by its fertilization envelope, but uptake
is clearly evidenced in the mature embryo by the highly
microvillous cell surface between the ciliary bases. Cilia fi ll
the space between the embryophore and the late embryo in
which the fertilization envelope is no longer seen. Finally,
Hughes suggested that ovicells evolved as merely protective
structures, later transforming into a site for accessory nutrition in some species.
A number of papers on cheilostome life cycles and reproductive ecology were also published in the 1980s and 1990s.
Researchers included Winston ( 1982 , 1983 , 1985 , 1988 )
Jackson and Wertheimer ( 1985 ), David Hughes ( 1989 ),
d’Hondt ( 1994 ), Roger Hughes and coauthors (Hughes and
Hughes 1987 ; Hunter and Hughes 1993 ; Hunter et al. 1996 ;
Wright and Hughes 2002 ) and Cancino with coauthors
(Cancino 1986 ; Cancino and Hughes 1987 ; Cancino et al.
1991 ), who mainly worked on Celleporella hyalina .
Experimental studies by the latter authors on isolated colonies of two species showed that self-fertilisation was either
impossible (oogenesis failed to complete in Membranipora
isabelleana or never started in C . hyalina ) (Cancino et al.
1991 ) or led to frequent embryo abortion and reduced offspring fi tness (Hunter and Hughes 1993 ). Inbreeding capability resulting in normal progeny was recorded only within
the Celleporella angusta clade (Hughes et al. 2002a ; Hughes
and Wright, in press ). Finally, it was concluded that outbreeding is the rule in this species and occasional selfi ng
might be connected with reduced opportunity for outbreeding in some instances. Sperm liberation (often synchronous
in stagnant or low-fl ow conditions) from the central, longest
tentacle of male zooids was observed, their lophophores
bending to release sperm towards the exhalant currents of
adjacent feeding lophophores. Evidence was obtained that C .
hyalina might store alien sperm (Hoare et al. 1999 ; Hunter
and Hughes 1995 ; Manríquez et al. 2001 ). Moreover, the
mechanisms of allosperm storage and translocation were
already present at the three-zooid stage of astogeny: colonies
consisting merely of the ancestrula and two autozooids
obtained and stored alien sperm, using it to fertilize eggs for
a maximum period of 3–6 weeks (Hughes et al. 2002b ).
Returning to the earlier idea of Marcus ( 1938a ), it was suggested that sperm can migrate through the colony from autozooids to females via communication pores, using the
funicular system (Manríquez et al. 2002 ). Further research
revealed that egg growth is absent in reproductively isolated
colonies, and allosperm is a trigger of vitellogenesis (Bishop
et al. 2000 ). Additionally, it was shown that some of the basal
and frontal autozooids become male after polypide cycling
in Celleporella hyalina (Cancino and Hughes 1988 ). Similar
changes, presumably connected with polypide recycling,
were described by Rogick ( 1956 ) and Powell ( 1967b ) in
Antarctothoa bougainvillei and A . delta (both as Hippothoa ),
respectively. Sex reversal also sometimes happens in A . bougainvillei : some female zooids change to males. In both
cases, these events involve obvious skeletal changes.
More recent publications include those by Wood and Seed
( 1992 ) on reproduction in the ctenostomes Alcyonidium hirsutum and Flustrellidra hispida growing together on algal
fronds and Barnes and Clarke ( 1998 ) on seasonality of polypide cycling and sexual reproduction in three Antarctic
cheilostomes. A review on the reproductive strategies of epialgal bryozoans was published by Seed and Hughes ( 1992 ).
Reed ( 1988 ) investigated reproduction in the ctenostomes Bowerbankia gracilis and B . aggregata (as gracilis
var. aggregata ) in detail, greatly supplementing the original
observations of Braem ( 1951 ). Both spermatogenesis and
oogenesis were described. Autozooids are protandrous hermaphrodites, developing their gonads asynchronously.
Thus, there may be functional male and female zooids
within the colony at the same time. Spermatogenic tissue
develops on the proximolateral cystid wall in connection
with a funicular cord. However, it sometimes covers the caecum and gizzard of the polypide. Formation of the ovary
occurs during polypide degeneration and is accompanied by
the appearance of a ciliated gutter that will be involved in
ovulation and oviposition. Ovary development on the lateral
cystid wall is served by a funicular strand and is not directly
associated with the degenerating polypide. However, it is
suggested that nutrients can be transferred from the polypide to the ovary via the funiculus. The mature ovary is said
to contain 1–2 vitellogenic [macrolecithal] and several previtellogenic oocytes that develop sequentially. The ovary
wall consists of squamous (enveloping previtellogenetic
oocytes) and cuboidal (enveloping vitellogenetic ones) follicle epithelium. Using TEM, Reed described the ultrastructure and the changes occurring in the oocytes and follicle
cells during oogenesis. It was shown that, during the vitellogenetic phase, the follicle cells are enlarged and transform
from squamous to cuboidal, actively producing and secreting proteinases into the narrow space around the vitellogenic oocyte, which is consumed by endocytosis. Reed
( 1991 ) noted that the follicle epithelium may synthesize
yolk precursors or modify them. He suggested that the
oocyte might also be able to synthesize yolk. Ovulation is
accompanied by the activity of the ciliary gutter that further
transfers the egg to the tentacle sheath, presumably via the
supraneural coelomopore. Similar organs were described by
Matricon (1963) in the ctenostome Alcyonidium polyoum
Appendices
Following oviposition, the embryo increases in volume 15.6
times, receiving extraembryonic nutrition in the ovicell.
Initially it is not in contact with the distal wall of the
maternal zooid, which consists of hypertrophied embryophore epithelium covered with a two- layered cuticle. Despite
this barrier, soluble nutrients are obviously released to the
fl uid in the brooding space, where they are taken up by the
embryo. There is no evidence of pinocytosis in the early
embryo surrounded by its fertilization envelope, but uptake
is clearly evidenced in the mature embryo by the highly
microvillous cell surface between the ciliary bases. Cilia fi ll
the space between the embryophore and the late embryo in
which the fertilization envelope is no longer seen. Finally,
Hughes suggested that ovicells evolved as merely protective
structures, later transforming into a site for accessory nutrition in some species.
A number of papers on cheilostome life cycles and reproductive ecology were also published in the 1980s and 1990s.
Researchers included Winston ( 1982 , 1983 , 1985 , 1988 )
Jackson and Wertheimer ( 1985 ), David Hughes ( 1989 ),
d’Hondt ( 1994 ), Roger Hughes and coauthors (Hughes and
Hughes 1987 ; Hunter and Hughes 1993 ; Hunter et al. 1996 ;
Wright and Hughes 2002 ) and Cancino with coauthors
(Cancino 1986 ; Cancino and Hughes 1987 ; Cancino et al.
1991 ), who mainly worked on Celleporella hyalina .
Experimental studies by the latter authors on isolated colonies of two species showed that self-fertilisation was either
impossible (oogenesis failed to complete in Membranipora
isabelleana or never started in C . hyalina ) (Cancino et al.
1991 ) or led to frequent embryo abortion and reduced offspring fi tness (Hunter and Hughes 1993 ). Inbreeding capability resulting in normal progeny was recorded only within
the Celleporella angusta clade (Hughes et al. 2002a ; Hughes
and Wright, in press ). Finally, it was concluded that outbreeding is the rule in this species and occasional selfi ng
might be connected with reduced opportunity for outbreeding in some instances. Sperm liberation (often synchronous
in stagnant or low-fl ow conditions) from the central, longest
tentacle of male zooids was observed, their lophophores
bending to release sperm towards the exhalant currents of
adjacent feeding lophophores. Evidence was obtained that C .
hyalina might store alien sperm (Hoare et al. 1999 ; Hunter
and Hughes 1995 ; Manríquez et al. 2001 ). Moreover, the
mechanisms of allosperm storage and translocation were
already present at the three-zooid stage of astogeny: colonies
consisting merely of the ancestrula and two autozooids
obtained and stored alien sperm, using it to fertilize eggs for
a maximum period of 3–6 weeks (Hughes et al. 2002b ).
Returning to the earlier idea of Marcus ( 1938a ), it was suggested that sperm can migrate through the colony from autozooids to females via communication pores, using the
funicular system (Manríquez et al. 2002 ). Further research
revealed that egg growth is absent in reproductively isolated
colonies, and allosperm is a trigger of vitellogenesis (Bishop
et al. 2000 ). Additionally, it was shown that some of the basal
and frontal autozooids become male after polypide cycling
in Celleporella hyalina (Cancino and Hughes 1988 ). Similar
changes, presumably connected with polypide recycling,
were described by Rogick ( 1956 ) and Powell ( 1967b ) in
Antarctothoa bougainvillei and A . delta (both as Hippothoa ),
respectively. Sex reversal also sometimes happens in A . bougainvillei : some female zooids change to males. In both
cases, these events involve obvious skeletal changes.
More recent publications include those by Wood and Seed
( 1992 ) on reproduction in the ctenostomes Alcyonidium hirsutum and Flustrellidra hispida growing together on algal
fronds and Barnes and Clarke ( 1998 ) on seasonality of polypide cycling and sexual reproduction in three Antarctic
cheilostomes. A review on the reproductive strategies of epialgal bryozoans was published by Seed and Hughes ( 1992 ).
Reed ( 1988 ) investigated reproduction in the ctenostomes Bowerbankia gracilis and B . aggregata (as gracilis
var. aggregata ) in detail, greatly supplementing the original
observations of Braem ( 1951 ). Both spermatogenesis and
oogenesis were described. Autozooids are protandrous hermaphrodites, developing their gonads asynchronously.
Thus, there may be functional male and female zooids
within the colony at the same time. Spermatogenic tissue
develops on the proximolateral cystid wall in connection
with a funicular cord. However, it sometimes covers the caecum and gizzard of the polypide. Formation of the ovary
occurs during polypide degeneration and is accompanied by
the appearance of a ciliated gutter that will be involved in
ovulation and oviposition. Ovary development on the lateral
cystid wall is served by a funicular strand and is not directly
associated with the degenerating polypide. However, it is
suggested that nutrients can be transferred from the polypide to the ovary via the funiculus. The mature ovary is said
to contain 1–2 vitellogenic [macrolecithal] and several previtellogenic oocytes that develop sequentially. The ovary
wall consists of squamous (enveloping previtellogenetic
oocytes) and cuboidal (enveloping vitellogenetic ones) follicle epithelium. Using TEM, Reed described the ultrastructure and the changes occurring in the oocytes and follicle
cells during oogenesis. It was shown that, during the vitellogenetic phase, the follicle cells are enlarged and transform
from squamous to cuboidal, actively producing and secreting proteinases into the narrow space around the vitellogenic oocyte, which is consumed by endocytosis. Reed
( 1991 ) noted that the follicle epithelium may synthesize
yolk precursors or modify them. He suggested that the
oocyte might also be able to synthesize yolk. Ovulation is
accompanied by the activity of the ciliary gutter that further
transfers the egg to the tentacle sheath, presumably via the
supraneural coelomopore. Similar organs were described by
Matricon (1963) in the ctenostome Alcyonidium polyoum
Appendices