305
Bantariella cookae (as Mimosella ). Since the volume of the
embryo increases markedly during development, one can
assume that extraembryonic nutrition occurs in this species.
Similar enlargement was depicted by Joliet ( 1877a ) in
Walkeria uva (as Valkeria cuscuta ).
Ström ( 1969 ) discovered external brooding in the ctenostome Triticella fl ava (as T . koreni ), strongly reminiscent of
the situation in Paludicella articulata (see Braem 1896 ).
Later a similar type of brooding was also described in
Panolicella nutans by Jebram ( 1985 ). However, in contrast
with P . articulata , there are up to 20 embryos in the sticky
fertilization envelopes that attach to the maternal zooid in
Triticella (see also Eggleston 1971 ). Only early development takes place in such a position (Ström 1977 ). Ström
additionally found that both testis and ovary are situated on
the dorsal cystid wall in the proximal half of the zooid (with
the ovary more distal). Up to 60 ovulated eggs are accumulated in the coelom prior to spawning, which occurs [via the
coelomopore] between the base of the dorsal tentacles.
Since spermatozoids attached to the tentacles of the
expanded lophophores were detected, Ström suggested that
cross-fertilization occurs in this species. He also showed
that two polar bodies are formed within the fertilization
envelope after egg release (Ström 1969 ). He additionally
described larval development and ancestrula formation.
Castric-Fey ( 1971 ) recorded the presence of an intertentacular organ in Alcyonidium argyllaceum .
Cook published a series of papers dealing with early larval development in several malacostegan cheilostomes. In
Einhornia crustulenta (as Electra ) and Conopeum seurati
(as Membranipora ) she observed formation and functioning
of the intertentacular organ. In the former species Cook
described defl ecting behaviour of the tentacles during egg
extrusion (when tentacles were defl ected to a position parallel to the frontal wall). The intertentacular organ was protruded as far as possible above the surface of the colony
(Cook 1960 , 1962 ). Egg liberation through the intertentacular organ was also recorded in Electra monostachys and
Conopeum reticulum (Cook 1964a ). The number of eggs per
zooid, their average size and the duration of egg extrusion
were all measured. Cook ( 1964b , 1968 ) recorded internal
brooding in the cheilostome Steginoporella buskii (as
Steganoporella ), noting that the polypide degenerates and
the cryptocyst is strongly reduced as the egg grows. She
found that there is a direct correlation between the size of the
egg [called an embryo in her 1968 paper] and reduction of
the zooidal cryptocyst.
Silén ( 1966 ) published a landmark paper in which he
described the liberation of sperm via the terminal pores of
the two distomedial tentacles in the malacostegans Electra
posidoniae , E. pilosa , Einhornia crustulenta (as Electra )
and Membranipora membranacea . The long-standing
enigma of bryozoan cross-fertilization was solved, although
many questions remained. All of the main events of gonadoand gametogenesis and their duration, as well as the later
destiny of the sex cells, were followed by observing live
colonies kept in aquaria. In E. posidoniae and E. crustulenta colonies consist of hermaphrodite zooids that are
either protandrous or, occasionally, simultaneous. There
are also males developing towards the end of reproduction
in E . posidoniae . Colonies of E. pilosa and M. membranacea were described as protandrous [i.e. consistng of simultaneous hermaphrodite zooids]. In the two former species,
spermatogenic tissue develops over lateral and proximal
parts of the frontal wall and on the lateral cystid walls. The
ovary is placed proximally on the funiculus, and usually
8–9 (up to 20) eggs are developed in E . posidoniae , while
six are depicted in Silén’s fi gure 5 of E . crustulenta . An
intertentacular organ develops only in the existing polypide
of hermaphrodite zooids when they reach maturity.
Evacuation of both eggs and sperm may be synchronized
over large parts of the colony (observed in M. membranacea by Zimmer who also saw synchronous spawning among
male zooids in a species of Schizoporella (personal communication in Reed 1991 )), often involving several neighbouring colonies. However, sperm and eggs are released
non-simultaneously in the same colony. Lophophores liberating sperm may sometimes remain everted for several
hours. Spermatozoids from the body cavity travel along the
lumina of the two dorsomedial tentacles, escape from them
via their terminal pores, and then drift away with the seawater. Being captured by the feeding current of a nearby
lophophore, they actively stick to the non-ciliated surface
of the tentacles then move towards the intertentacular organ
at about the same time that eggs enter it in E . posidoniae . In
E . crustulenta , sperm were observed inside the intertentacular organ. Silén ascribed an important role to chemotaxis
as spermatozoids “search for” the egg. A fertilization envelope appears approximately 1 h after egg release. Based on
these observations, Silén suggested that fertilization takes
place externally in the fi rst species and inside the intertentacular organ in the second. Nevertheless, Silén admitted
that, theoretically, sperm could also enter the zooid cavity
through the intertentacular organ or supraneural pore and
cross-fertilization could occur in the body cavity. Returning
to the earlier idea of Joliet ( 1877a ), Silén speculated that
fertilization in larviparous forms could be achieved during
oviposition. Strangely, the data of Marcus ( 1938a ), who
discovered precocious intraovarian fertilization in brooding
Gymnolaemata, were overlooked or ignored, despite his
paper being cited. Silén’s ( 1944 ) own fi nding of male nuclei
inside ovulated oocytes in Labiostomella gisleni was not
mentioned or discussed either.
Bullivant ( 1967 ) confi rmed the data of Silén, recording
sperm release through the terminal pores of all the tentacles
in the ctenostome Zoobotryon verticillatum and the cheilostome Schizoporella unicornis . Except for “passive” evacuation, numerous spermatozoids were released on retraction of
Appendices
Bantariella cookae (as Mimosella ). Since the volume of the
embryo increases markedly during development, one can
assume that extraembryonic nutrition occurs in this species.
Similar enlargement was depicted by Joliet ( 1877a ) in
Walkeria uva (as Valkeria cuscuta ).
Ström ( 1969 ) discovered external brooding in the ctenostome Triticella fl ava (as T . koreni ), strongly reminiscent of
the situation in Paludicella articulata (see Braem 1896 ).
Later a similar type of brooding was also described in
Panolicella nutans by Jebram ( 1985 ). However, in contrast
with P . articulata , there are up to 20 embryos in the sticky
fertilization envelopes that attach to the maternal zooid in
Triticella (see also Eggleston 1971 ). Only early development takes place in such a position (Ström 1977 ). Ström
additionally found that both testis and ovary are situated on
the dorsal cystid wall in the proximal half of the zooid (with
the ovary more distal). Up to 60 ovulated eggs are accumulated in the coelom prior to spawning, which occurs [via the
coelomopore] between the base of the dorsal tentacles.
Since spermatozoids attached to the tentacles of the
expanded lophophores were detected, Ström suggested that
cross-fertilization occurs in this species. He also showed
that two polar bodies are formed within the fertilization
envelope after egg release (Ström 1969 ). He additionally
described larval development and ancestrula formation.
Castric-Fey ( 1971 ) recorded the presence of an intertentacular organ in Alcyonidium argyllaceum .
Cook published a series of papers dealing with early larval development in several malacostegan cheilostomes. In
Einhornia crustulenta (as Electra ) and Conopeum seurati
(as Membranipora ) she observed formation and functioning
of the intertentacular organ. In the former species Cook
described defl ecting behaviour of the tentacles during egg
extrusion (when tentacles were defl ected to a position parallel to the frontal wall). The intertentacular organ was protruded as far as possible above the surface of the colony
(Cook 1960 , 1962 ). Egg liberation through the intertentacular organ was also recorded in Electra monostachys and
Conopeum reticulum (Cook 1964a ). The number of eggs per
zooid, their average size and the duration of egg extrusion
were all measured. Cook ( 1964b , 1968 ) recorded internal
brooding in the cheilostome Steginoporella buskii (as
Steganoporella ), noting that the polypide degenerates and
the cryptocyst is strongly reduced as the egg grows. She
found that there is a direct correlation between the size of the
egg [called an embryo in her 1968 paper] and reduction of
the zooidal cryptocyst.
Silén ( 1966 ) published a landmark paper in which he
described the liberation of sperm via the terminal pores of
the two distomedial tentacles in the malacostegans Electra
posidoniae , E. pilosa , Einhornia crustulenta (as Electra )
and Membranipora membranacea . The long-standing
enigma of bryozoan cross-fertilization was solved, although
many questions remained. All of the main events of gonadoand gametogenesis and their duration, as well as the later
destiny of the sex cells, were followed by observing live
colonies kept in aquaria. In E. posidoniae and E. crustulenta colonies consist of hermaphrodite zooids that are
either protandrous or, occasionally, simultaneous. There
are also males developing towards the end of reproduction
in E . posidoniae . Colonies of E. pilosa and M. membranacea were described as protandrous [i.e. consistng of simultaneous hermaphrodite zooids]. In the two former species,
spermatogenic tissue develops over lateral and proximal
parts of the frontal wall and on the lateral cystid walls. The
ovary is placed proximally on the funiculus, and usually
8–9 (up to 20) eggs are developed in E . posidoniae , while
six are depicted in Silén’s fi gure 5 of E . crustulenta . An
intertentacular organ develops only in the existing polypide
of hermaphrodite zooids when they reach maturity.
Evacuation of both eggs and sperm may be synchronized
over large parts of the colony (observed in M. membranacea by Zimmer who also saw synchronous spawning among
male zooids in a species of Schizoporella (personal communication in Reed 1991 )), often involving several neighbouring colonies. However, sperm and eggs are released
non-simultaneously in the same colony. Lophophores liberating sperm may sometimes remain everted for several
hours. Spermatozoids from the body cavity travel along the
lumina of the two dorsomedial tentacles, escape from them
via their terminal pores, and then drift away with the seawater. Being captured by the feeding current of a nearby
lophophore, they actively stick to the non-ciliated surface
of the tentacles then move towards the intertentacular organ
at about the same time that eggs enter it in E . posidoniae . In
E . crustulenta , sperm were observed inside the intertentacular organ. Silén ascribed an important role to chemotaxis
as spermatozoids “search for” the egg. A fertilization envelope appears approximately 1 h after egg release. Based on
these observations, Silén suggested that fertilization takes
place externally in the fi rst species and inside the intertentacular organ in the second. Nevertheless, Silén admitted
that, theoretically, sperm could also enter the zooid cavity
through the intertentacular organ or supraneural pore and
cross-fertilization could occur in the body cavity. Returning
to the earlier idea of Joliet ( 1877a ), Silén speculated that
fertilization in larviparous forms could be achieved during
oviposition. Strangely, the data of Marcus ( 1938a ), who
discovered precocious intraovarian fertilization in brooding
Gymnolaemata, were overlooked or ignored, despite his
paper being cited. Silén’s ( 1944 ) own fi nding of male nuclei
inside ovulated oocytes in Labiostomella gisleni was not
mentioned or discussed either.
Bullivant ( 1967 ) confi rmed the data of Silén, recording
sperm release through the terminal pores of all the tentacles
in the ctenostome Zoobotryon verticillatum and the cheilostome Schizoporella unicornis . Except for “passive” evacuation, numerous spermatozoids were released on retraction of
Appendices