145
developing larvae were observed by Jullien ( 1888 ) inside
zooids of Beania costata (as Diachoris ). Later Calvet ( 1900 )
described the internal brood chamber (pouch or diverticulum
of the vestibulum) in C . pallasiana , noting the muscles
attached to its walls and the “membrane vitelline” [fertilization
envelope] surrounding the early embryo. A similar “ovisac”
“with delicate walls” and “inserted muscle-fi bres” was
recorded “at the distal end of the zooecium” in Cheiloporina
haddoni (as Lepralia ) by Harmer ( 1902 , p. 300).
Waters ( 1909 , 1912 , 1913 ) recorded internal brooding in
Watersipora (as Lepralia ), Adeona , Adeonella , Adeonellopsis ,
Laminopora , Beania , Poricellaria and Catenicella (as
Vittaticella ) and discussed the possible value of brood chambers for bryozoan classifi cation. Embryos were said to be
brooded inside an internal “sac near the distal end of
the zooecium” – a specialized enlarged “gonoecium” in
Adeonidae. Incubation sacs were also found in Beania (see
Waters 1912 , pp. 492–493). This author termed the internal
brood sac of Watersipora cucullata (as Lepralia ) “a concealed ovicell” (Waters 1909 , p. 151)
Waters ( 1913 , p. 500) found membrane-bounded embryos
in Steginoporella magnilabris (as Steganoporella ), referring
to them as “internal ovicells”. He also found an internally
brooded embryo in Chlidonia pyriformis (as C. cordieri ) in
sections, but gave no details about structure. Marcus ( 1922 )
made a similar fi nding while studying Steginoporella haddoni
(as Steganoporella ). Harmer ( 1926 , p. 271) described internal
brooding in “a spacious, thin-walled ovisac” in S. magnilabris (as Steganoporella ) that extended almost to the zooidal
basal wall, attaching “to the lateral walls … by a number of
muscle-fi bres”, but was unable to determine if it was connected with the vestibulum. Studying the same species, Cook
( 1964 , pp. 52–53) stated “when the egg [i.e. embryo] has
reached the largest size observed it can be seen beneath the
operculum within the ovisac which is attached to the lateral
walls of the zooecium.”
Hastings ( 1944 , pp. 273–274) recorded “zooecia … [with]
embryos in the body-cavity, although they had no ovicells
and showed no external difference from the non-fertile zooecia” in Oshurkovia littoralis (as Umbonula ). Hastings ( 1964 ,
p. 251) subsequently referred to “internal ovisacs” in this
species, confi rmed by Eggleston ( 1972 ) who noted simultaneous internal brooding of several embryos. The structure of
the brooding apparatus is unknown, however.
Mawatari ( 1952 , p. 20) studied aspects of sexual reproduction in Watersipora subtorquata (as W . cucullata ). He mentioned “the embryo sac” enveloping the developing embryo;
his fi gures 34–35 and 44 show it to be an evagination of
the vestibulum, confi rmed by Zimmer (personal communication in
Reed 1991 ) for W. arcuata . Similarly, Cook ( 1979 , p. 200)
mentioned “membranous diverticula housed within zooid body
wall” as a brood chamber in dimorphic female zooids of
Tropidozoum cellariiforme . According to Gordon and Mawatari
( 1992 ), internal brooding is characteristic of Chaperia granulosa (Chaperiidae) (reviewed in Ostrovsky 2008b ).
My data have contributed to further understanding of the
anatomy of cheilostome internal brooding. In addition to the
calloporid genus Cauloramphus (see Sect. 2.3.1 ), a number of
species with internal incubation sacs were studied from the
families Calloporidae, Cupuladriidae, Flustridae, Beaniidae,
Steginoporellidae, Chlidoniidae, Romancheinidae, Watersiporidae, Cryptosulidae, Euthyrisellidae and Urceoliporidae
(Ostrovsky 2009 ; Ostrovsky et al. 2006 , 2007 , 2009a , b and
unpublished data).
In Nematofl ustra fl agellata (Flustridae), the brooding
zooid differs in external appearance from non-brooding
ones. The frontally visible inner vesicle (a presumed homologue of the ooecial vesicle in an ovicell-bearing ancestor) is
a hollow fold of the distal wall of the maternal autozooid that
adjoins the arched proximal wall of the distal autozooid
(Fig. 2.46A ). The entrance to the brood sac is closed by this
vesicle, which, displaced, allows the brood cavity to communicate directly with the environment rather than the vestibulum. The vesicle bears a large sclerite, attached to which
is a group of muscles that open the entrance to the brood sac
during oviposition and larval release. These muscles are
anchored to the cystid basal wall behind the proximal end of
the brood sac. This sac is a voluminous oval invagination of
the non-calcifi ed distal wall of the maternal autozooid and
consists of a capacious chamber and a neck that tapers
towards the opening. The sac wall is thin and easily deformed,
being composed of a cuticular layer and underlying fl at epithelial cells. The muscle bundles that change the shape of the
sac during oviposition and larval release are attached to its
wall proximally and distally. The lower ends of the muscle
bundles are attached to the basal and transverse walls of the
cystid (Fig. 2.46A ).
In “ Bifl ustra ” perfragilis (family incertae sedis) and
Gontarella sp. (?Calloporidae) (Fig. 2.46B, C ), brooding
zooids cannot be externally distinguished from non- brooding
ones. The opening of the incubation sac is closed by the
upper part of the distal wall of the maternal autozooid playing the role of the inner vesicle. Wall cuticle is thicker in this
area but there is no sclerite. As in Nematofl ustra , the brood
cavity communicates with the environment independently of
the vestibulum and is not closed by the zooidal operculum.
The neck of the brood sac is very short in “ B .” perfragilis and
long in Gontarella sp.
The brood-sac neck is also long in Beania bilaminata
(Beaniidae) (Fig. 1.22 ). A brood chamber containing a
late embryo occupies most of the coelom of the maternal
autozooid. The chamber opening communicates with the
environment independently of the vestibulum and is normally
closed by an ooecial vesicle with a sclerite and stout muscle
bundles. Strikingly, the ooecium in Beania is developed to
varying degrees in different species studied. In Beania sp. it
2.3 Structure and Development of Brood Chambers in Cheilostomata
developing larvae were observed by Jullien ( 1888 ) inside
zooids of Beania costata (as Diachoris ). Later Calvet ( 1900 )
described the internal brood chamber (pouch or diverticulum
of the vestibulum) in C . pallasiana , noting the muscles
attached to its walls and the “membrane vitelline” [fertilization
envelope] surrounding the early embryo. A similar “ovisac”
“with delicate walls” and “inserted muscle-fi bres” was
recorded “at the distal end of the zooecium” in Cheiloporina
haddoni (as Lepralia ) by Harmer ( 1902 , p. 300).
Waters ( 1909 , 1912 , 1913 ) recorded internal brooding in
Watersipora (as Lepralia ), Adeona , Adeonella , Adeonellopsis ,
Laminopora , Beania , Poricellaria and Catenicella (as
Vittaticella ) and discussed the possible value of brood chambers for bryozoan classifi cation. Embryos were said to be
brooded inside an internal “sac near the distal end of
the zooecium” – a specialized enlarged “gonoecium” in
Adeonidae. Incubation sacs were also found in Beania (see
Waters 1912 , pp. 492–493). This author termed the internal
brood sac of Watersipora cucullata (as Lepralia ) “a concealed ovicell” (Waters 1909 , p. 151)
Waters ( 1913 , p. 500) found membrane-bounded embryos
in Steginoporella magnilabris (as Steganoporella ), referring
to them as “internal ovicells”. He also found an internally
brooded embryo in Chlidonia pyriformis (as C. cordieri ) in
sections, but gave no details about structure. Marcus ( 1922 )
made a similar fi nding while studying Steginoporella haddoni
(as Steganoporella ). Harmer ( 1926 , p. 271) described internal
brooding in “a spacious, thin-walled ovisac” in S. magnilabris (as Steganoporella ) that extended almost to the zooidal
basal wall, attaching “to the lateral walls … by a number of
muscle-fi bres”, but was unable to determine if it was connected with the vestibulum. Studying the same species, Cook
( 1964 , pp. 52–53) stated “when the egg [i.e. embryo] has
reached the largest size observed it can be seen beneath the
operculum within the ovisac which is attached to the lateral
walls of the zooecium.”
Hastings ( 1944 , pp. 273–274) recorded “zooecia … [with]
embryos in the body-cavity, although they had no ovicells
and showed no external difference from the non-fertile zooecia” in Oshurkovia littoralis (as Umbonula ). Hastings ( 1964 ,
p. 251) subsequently referred to “internal ovisacs” in this
species, confi rmed by Eggleston ( 1972 ) who noted simultaneous internal brooding of several embryos. The structure of
the brooding apparatus is unknown, however.
Mawatari ( 1952 , p. 20) studied aspects of sexual reproduction in Watersipora subtorquata (as W . cucullata ). He mentioned “the embryo sac” enveloping the developing embryo;
his fi gures 34–35 and 44 show it to be an evagination of
the vestibulum, confi rmed by Zimmer (personal communication in
Reed 1991 ) for W. arcuata . Similarly, Cook ( 1979 , p. 200)
mentioned “membranous diverticula housed within zooid body
wall” as a brood chamber in dimorphic female zooids of
Tropidozoum cellariiforme . According to Gordon and Mawatari
( 1992 ), internal brooding is characteristic of Chaperia granulosa (Chaperiidae) (reviewed in Ostrovsky 2008b ).
My data have contributed to further understanding of the
anatomy of cheilostome internal brooding. In addition to the
calloporid genus Cauloramphus (see Sect. 2.3.1 ), a number of
species with internal incubation sacs were studied from the
families Calloporidae, Cupuladriidae, Flustridae, Beaniidae,
Steginoporellidae, Chlidoniidae, Romancheinidae, Watersiporidae, Cryptosulidae, Euthyrisellidae and Urceoliporidae
(Ostrovsky 2009 ; Ostrovsky et al. 2006 , 2007 , 2009a , b and
unpublished data).
In Nematofl ustra fl agellata (Flustridae), the brooding
zooid differs in external appearance from non-brooding
ones. The frontally visible inner vesicle (a presumed homologue of the ooecial vesicle in an ovicell-bearing ancestor) is
a hollow fold of the distal wall of the maternal autozooid that
adjoins the arched proximal wall of the distal autozooid
(Fig. 2.46A ). The entrance to the brood sac is closed by this
vesicle, which, displaced, allows the brood cavity to communicate directly with the environment rather than the vestibulum. The vesicle bears a large sclerite, attached to which
is a group of muscles that open the entrance to the brood sac
during oviposition and larval release. These muscles are
anchored to the cystid basal wall behind the proximal end of
the brood sac. This sac is a voluminous oval invagination of
the non-calcifi ed distal wall of the maternal autozooid and
consists of a capacious chamber and a neck that tapers
towards the opening. The sac wall is thin and easily deformed,
being composed of a cuticular layer and underlying fl at epithelial cells. The muscle bundles that change the shape of the
sac during oviposition and larval release are attached to its
wall proximally and distally. The lower ends of the muscle
bundles are attached to the basal and transverse walls of the
cystid (Fig. 2.46A ).
In “ Bifl ustra ” perfragilis (family incertae sedis) and
Gontarella sp. (?Calloporidae) (Fig. 2.46B, C ), brooding
zooids cannot be externally distinguished from non- brooding
ones. The opening of the incubation sac is closed by the
upper part of the distal wall of the maternal autozooid playing the role of the inner vesicle. Wall cuticle is thicker in this
area but there is no sclerite. As in Nematofl ustra , the brood
cavity communicates with the environment independently of
the vestibulum and is not closed by the zooidal operculum.
The neck of the brood sac is very short in “ B .” perfragilis and
long in Gontarella sp.
The brood-sac neck is also long in Beania bilaminata
(Beaniidae) (Fig. 1.22 ). A brood chamber containing a
late embryo occupies most of the coelom of the maternal
autozooid. The chamber opening communicates with the
environment independently of the vestibulum and is normally
closed by an ooecial vesicle with a sclerite and stout muscle
bundles. Strikingly, the ooecium in Beania is developed to
varying degrees in different species studied. In Beania sp. it
2.3 Structure and Development of Brood Chambers in Cheilostomata