303
begun in connection with sexual reproduction in order to
empty the genital cells and supply food for the growing
brood” (p. 375). Another of his conclusions was that the formation of an intertentacular organ is indispensably combined
with polypide replacement. Later Silén ( 1966 ), studying living material, challenged this statement because he observed
that this organ forms in the existing polypide upon maturation of eggs and this was further supported by Jebram
( 1973 ), Hageman ( 1981 ) and Cadman and Ryland ( 1996 ).
Corrêa ( 1948 ) studied reproduction in the cheilostome
Bugula foliolata (as B. fl abellata ), describing colonial
zonality, based on the polypide and sexual cycling. She
observed spermato- and oogenesis, developing ovicells,
the oviposition of the mature egg into the ovicell, and
development and regression of the hypertrophied epithelium of the ooecial vesicle [embryophore] in relation to the
onset and completion of brooding. The supraneural pore
was stated to occur in both fertile and sterile zooids. She
also found sperm heads in early intraovarian oocytes in
accordance with the fi ndings of Marcus ( 1938a , 1941a ),
terming the eggs oligolecithal-homolecithal and stating
that early and monospermic fertilization “is almost certainly realized by sperms of the same zooid” in this species
(Corrêa 1948 , p. 46). Intracolonial self-fertilization was
also suggested. Corrêa noted slight zooidal protandry in
hermaphrodite zooids. It was mentioned that 2–3 “ovocytes” simultaneously growing in the ovary have different
sizes. Egg maturation was said to occur in the zooid cavity.
Judging from her description, Corrêa thought that the fi rst
polar body is formed inside the zooid before transfer to the
ovicell together with the oocyte. Three polar bodies (“polocytes”) are shown after oviposition surrounded by the fertilization envelope, together with a zygote, in her
illustrations. Remarkably, Corrêa recorded two embryos in
the same ovicell at the same stage of cleavage and suggested that they were oviposited by the polypides of two
neighbouring zooids. Additionally, she found a supraneural pore in Bifl ustra arborescens (as Conopeum
commensale ).
Silén ( 1946 , 1947 ) discovered specialized brooding
zooids (“gonozooids”) with external incubation sacs in three
burrowing ctenostomes in the genus Penetrantia . According
to the original description, the wall of the brood sac is made
of cuticle, but its mode of formation and exact structure are
unclear. Silén termed it a “pouch of the exterior wall” ( 1947 ,
p. 20), suggesting that the “gonozooid was composed of two
zooids, an older, dead one and a younger, living one developed inside the former” (p. 34). Thus, the brood cavity was
explained as a space between two cuticular walls – external
(pertaining to the fi rst zooid in which epithelial cells had
vanished) and internal (belonging to the new zooid).
However, Ström ( 1977 , p. 34) speculated that the “brood
sac” may have been a “thickened embryonic membrane”
[fertilization envelope]. Additionally, Silén ( 1947 ) described
an ovary in P . densa , stating that the embryo begins development inside the zooid cavity, later being transferred to
the incubation pouch. He suggested three possible variations for oviposition, but further research is necessary to
elucidate brooding in this group. Silén ( 1947 ) also found an
embryo brooded within the tentacle sheath in Immergentia
californica .
Second Half of the Twentieth Century:
Extensive Reviews and New Discoveries
Soule and Soule largely confi rmed the fi ndings of Silén in
regard to Ctenostomata. A number of burrowing ctenostome
brooders with both types of brooding were described in a
series of papers (Soule 1950a , b ; Soule and Soule 1969a , b ,
1975 , 1976 ). They focused particularly on Penetrantia
(brooding in a “gonozoid”) and Spathipora , Immergentia
and Terebripora (brooding in the introvert). Bobin and
Prenant ( 1954 ) confi rmed the data of Soule, describing
brooding in the introvert in T . comma (for information on
reproduction and brooding in ctenostomes, see also Prenant
and Bobin ( 1956 ), d’Hondt ( 1983 ), and Hayward ( 1985 )).
Mawatari ( 1951a , b ) published two papers dealing with
the cheilostomes Bugula neritina and Tricellaria occidentalis (currently generally called T . inopinata but it may be T.
catalinensis ) respectively. In Bugula , zooids were described
as simultaneous hermaphrodites performing self- fertilization.
Mawatari studied embryogenesis, larval structure, larval
release and locomotion as well as larval attachment and
metamorphosis. He also presented data on the B. neritina life
cycle throughout the year, including peaks of reproduction
and larval settlement and the rate of colony growth and maturation. In Tricellaria , zooids were said to be nonsimultaneous hermaphrodites. Mawatari ( 1951b ) briefl y
described oogenesis, and it is clear from his text and illustrations that oocytes develop in pairs in this species.
The following year, Mawatari ( 1952 ) made a detailed
study of Watersipora subtorquata (as W . cucullata ).
According to his description, zooids are simultaneously hermaphrodite, which is why self-fertilization was considered
usual for this species. Spermatogenic tissue develops at different sites on the surface of the lateral and proximal transverse cystid walls and compensation sac. The ovary is
positioned on the lateral or transverse walls in the distal part
of the maternal zooid, and 4–5 oocytes were said to develop
within it. It is clear from Mawatari’s illustrations that they
are arranged in doublets. One or more sperm heads were
detected in the “developing egg”, but fertilization was stated
to be monospermic. The large leading oocyte ovulates,
“moves … under the vestibule, and is enveloped within the
embryo sac” ( 1952 , p. 20). Mawatari’s fi gures 20–38 and 44
Appendices
begun in connection with sexual reproduction in order to
empty the genital cells and supply food for the growing
brood” (p. 375). Another of his conclusions was that the formation of an intertentacular organ is indispensably combined
with polypide replacement. Later Silén ( 1966 ), studying living material, challenged this statement because he observed
that this organ forms in the existing polypide upon maturation of eggs and this was further supported by Jebram
( 1973 ), Hageman ( 1981 ) and Cadman and Ryland ( 1996 ).
Corrêa ( 1948 ) studied reproduction in the cheilostome
Bugula foliolata (as B. fl abellata ), describing colonial
zonality, based on the polypide and sexual cycling. She
observed spermato- and oogenesis, developing ovicells,
the oviposition of the mature egg into the ovicell, and
development and regression of the hypertrophied epithelium of the ooecial vesicle [embryophore] in relation to the
onset and completion of brooding. The supraneural pore
was stated to occur in both fertile and sterile zooids. She
also found sperm heads in early intraovarian oocytes in
accordance with the fi ndings of Marcus ( 1938a , 1941a ),
terming the eggs oligolecithal-homolecithal and stating
that early and monospermic fertilization “is almost certainly realized by sperms of the same zooid” in this species
(Corrêa 1948 , p. 46). Intracolonial self-fertilization was
also suggested. Corrêa noted slight zooidal protandry in
hermaphrodite zooids. It was mentioned that 2–3 “ovocytes” simultaneously growing in the ovary have different
sizes. Egg maturation was said to occur in the zooid cavity.
Judging from her description, Corrêa thought that the fi rst
polar body is formed inside the zooid before transfer to the
ovicell together with the oocyte. Three polar bodies (“polocytes”) are shown after oviposition surrounded by the fertilization envelope, together with a zygote, in her
illustrations. Remarkably, Corrêa recorded two embryos in
the same ovicell at the same stage of cleavage and suggested that they were oviposited by the polypides of two
neighbouring zooids. Additionally, she found a supraneural pore in Bifl ustra arborescens (as Conopeum
commensale ).
Silén ( 1946 , 1947 ) discovered specialized brooding
zooids (“gonozooids”) with external incubation sacs in three
burrowing ctenostomes in the genus Penetrantia . According
to the original description, the wall of the brood sac is made
of cuticle, but its mode of formation and exact structure are
unclear. Silén termed it a “pouch of the exterior wall” ( 1947 ,
p. 20), suggesting that the “gonozooid was composed of two
zooids, an older, dead one and a younger, living one developed inside the former” (p. 34). Thus, the brood cavity was
explained as a space between two cuticular walls – external
(pertaining to the fi rst zooid in which epithelial cells had
vanished) and internal (belonging to the new zooid).
However, Ström ( 1977 , p. 34) speculated that the “brood
sac” may have been a “thickened embryonic membrane”
[fertilization envelope]. Additionally, Silén ( 1947 ) described
an ovary in P . densa , stating that the embryo begins development inside the zooid cavity, later being transferred to
the incubation pouch. He suggested three possible variations for oviposition, but further research is necessary to
elucidate brooding in this group. Silén ( 1947 ) also found an
embryo brooded within the tentacle sheath in Immergentia
californica .
Second Half of the Twentieth Century:
Extensive Reviews and New Discoveries
Soule and Soule largely confi rmed the fi ndings of Silén in
regard to Ctenostomata. A number of burrowing ctenostome
brooders with both types of brooding were described in a
series of papers (Soule 1950a , b ; Soule and Soule 1969a , b ,
1975 , 1976 ). They focused particularly on Penetrantia
(brooding in a “gonozoid”) and Spathipora , Immergentia
and Terebripora (brooding in the introvert). Bobin and
Prenant ( 1954 ) confi rmed the data of Soule, describing
brooding in the introvert in T . comma (for information on
reproduction and brooding in ctenostomes, see also Prenant
and Bobin ( 1956 ), d’Hondt ( 1983 ), and Hayward ( 1985 )).
Mawatari ( 1951a , b ) published two papers dealing with
the cheilostomes Bugula neritina and Tricellaria occidentalis (currently generally called T . inopinata but it may be T.
catalinensis ) respectively. In Bugula , zooids were described
as simultaneous hermaphrodites performing self- fertilization.
Mawatari studied embryogenesis, larval structure, larval
release and locomotion as well as larval attachment and
metamorphosis. He also presented data on the B. neritina life
cycle throughout the year, including peaks of reproduction
and larval settlement and the rate of colony growth and maturation. In Tricellaria , zooids were said to be nonsimultaneous hermaphrodites. Mawatari ( 1951b ) briefl y
described oogenesis, and it is clear from his text and illustrations that oocytes develop in pairs in this species.
The following year, Mawatari ( 1952 ) made a detailed
study of Watersipora subtorquata (as W . cucullata ).
According to his description, zooids are simultaneously hermaphrodite, which is why self-fertilization was considered
usual for this species. Spermatogenic tissue develops at different sites on the surface of the lateral and proximal transverse cystid walls and compensation sac. The ovary is
positioned on the lateral or transverse walls in the distal part
of the maternal zooid, and 4–5 oocytes were said to develop
within it. It is clear from Mawatari’s illustrations that they
are arranged in doublets. One or more sperm heads were
detected in the “developing egg”, but fertilization was stated
to be monospermic. The large leading oocyte ovulates,
“moves … under the vestibule, and is enveloped within the
embryo sac” ( 1952 , p. 20). Mawatari’s fi gures 20–38 and 44
Appendices