136
(Figs. 2.7a (F) and 2.24 ), however, they should be classifi ed as
subimmersed. The ovicells are cleithral, i.e. the brood cavity is
closed by the ooecial vesicle, which is overlapped proximally
from above by the zooidal operculum. [Note that these ovicells are erroneously referred to as semicleithral in Ostrovsky
( 2008b ); but see Ostrovsky et al. ( 2009a ).] As in Wilbertopora ,
Bryocalyx and possibly Concertina , the ooecium consists of
two symmetric halves (lobes) separated by a transverse medial
suture easily seen in the interior and generally also the exterior
of the ooecium (see also Gordon ( 1986 , pl. 6A), showing the
developing ooecium). Its proximal edge is fl anked by a narrow
non- calcifi ed area.
On the inner surface of the ooecium, the medial suture
ends as a closed horizontal slit, more or less as in the cribrilinids Puellina , Figularia and Corbulipora (see Sect. 2.3.2 )
though somewhat different in shape. The adjoining lateral
surfaces of the ooecial lobes merge to form a two-layered longitudinal septum corresponding to the outer and inner medial
suture. As in Figularia , the ooecial coelomic cavity is represented by the lumen of each lobe communicating with each
other underneath the membranous wall of the non-calcifi ed
area on the proximal edge of the ooecium. The paired lumina
of the ooecium also communicate with the visceral coelom of
the parent zooid via two symmetric communication pores
situated directly below the ooecial lobes (Fig. 2.24 ). In
younger zooids they appear as non-parallel slits but later
transform into oval pores. Judging from the volume of the
ooecial coeloms and the size of the pores, the latter were open
in life, potentially allowing circulation of coelomic fl uid. It is
possible, however, that these pores later become plugged by
non- specialized epithelial cells (Ostrovsky et al. 2009a ).
The bases of the ooecial halves are rather narrow (in this
regard resembling the ovicells of extinct Wilbertopora , see
above). As the bases are formed, the lobes become broader.
Their lower edge grows proximally, fi rst adjoining the proximal gymnocyst of the distal zooid and then overgrowing the
lateral wall of the maternal zooid (see also Gordon ( 1986 , pl.
6A)). As in Wilbertopora , a suture remains between the
lower surface of the ooecial lobes and the zooidal surface.
Only about half the ovicell fl oor is represented by the
calcifi ed wall. The remaining half is formed by the thin noncalcifi ed distal wall of the maternal autozooid (Figs. 2.7a (F)
and 2.24 ). Its upper part forms the ooecial vesicle, the wall of
which has a thickened, sclerite-like, zone of cuticle. The
internal muscle bundles of the vesicle, inserting on its middle
and lower wall, effect opening of the ovicell by contracting
the vesicle. At their opposite ends, these bundles attach compactly to the basal wall of the maternal autozooid (Ostrovsky
et al. 2009a ).
2.3.1.6 Immersed Ovicells
Compared to Valdemunitella lata , the incubation chamber
of the immersed ovicell in Crassimarginatella sp. lies
completely in the distal part of the maternal autozooid
(Figs. 2.7b (B) and 2.25A ). The vestigial ooecium, slightly
protruding above the colony surface, is formed by the distal
autozooid (type 1, category A). It is represented by two
thick walls, the outer ectooecium and inner entooecium,
which fuse because of strong calcifi cation. Initially, the
coelom of the ooecium is a slit-like lumen lined with epithelial cells and communicating with the parent coelom via
an arched slit. Later, because of increased calcifi cation, the
ooecial coelom is reduced to a crescentic pit at the proximal
edge of the ooecium and the narrow canal that connects the
pit with the visceral coelom. The arched communication slit
becomes a closed groove with several pores or a single pore
at the bottom. In some old ooecia the communication canal
is completely closed and the pores at both ends are also not
retained.
The brood sac is a deep invagination of the distal wall of the
maternal autozooid (Figs. 2.7b (B) and 2.25A ). Distally, the
wall of the brood sac is attached to the transverse wall at
the base of the ooecium, whereas proximally it forms a kind of
ooecial vesicle overlapping the embryo from above. It was not
found to contain either a sclerite or specialized musculature,
and yet it closes the entrance to the brood cavity in the same
manner as an actual ooecial vesicle. Several muscle bundles
are attached to the sac wall in its proximal part, their opposite
ends being attached to the basal wall of the maternal autozooid.
They appear to extend the brood chamber during oviposition
and larval release. Immersed ovicells are also characteristic of
the calloporid genera Aplousina and Cranosina and the related
family Antroporidae (Ostrovsky et al. 2009a ).
2.3.1.7 Internal Brood Sac with Vestigial
Ooecium in Cauloramphus
In the genus Cauloramphus , all components of the brood
chamber are formed solely at the expense of the maternal
autozooid (type 2) (Ostrovsky 2008b ; Ostrovsky et al. 2007 ,
2009a ). The vestigial kenozooidal ooecium is budded at the
distal rim of the maternal autozooid, while its base merges
with the upper part of the distal wall of this zooid
(Figs. 2.6b (E), 2.7b (C), and 2.25B ). The ooecial cavity communicates with the visceral coelom via 1–3 communication
pores with pore-cell complexes (Fig. 2.25B ). The outer wall
of the ooecium (ectooecium) is uncalcifi ed except for its base
as a consequence of which, in cleaned specimens, it is mostly
entooecium that is visible, appearing as a prominent cap in
some species, while in Cauloramphus spinifer it appears as a
small plate with an arched outline. The ooecial cavity is a
deep groove. In older zooids, its lower part is partly reduced
by wall calcifi cation. This results in the formation of 1–3 coelomic canals, each leading to a communication pore. These
canals are connected with each other only in the upper part of
the ooecium, under the membranous area of the ectooecium.
The lumina of these canals are partly fi lled with loose epithelial
2 Cheilostome Brood Chambers: Structure, Formation, Evolution
(Figs. 2.7a (F) and 2.24 ), however, they should be classifi ed as
subimmersed. The ovicells are cleithral, i.e. the brood cavity is
closed by the ooecial vesicle, which is overlapped proximally
from above by the zooidal operculum. [Note that these ovicells are erroneously referred to as semicleithral in Ostrovsky
( 2008b ); but see Ostrovsky et al. ( 2009a ).] As in Wilbertopora ,
Bryocalyx and possibly Concertina , the ooecium consists of
two symmetric halves (lobes) separated by a transverse medial
suture easily seen in the interior and generally also the exterior
of the ooecium (see also Gordon ( 1986 , pl. 6A), showing the
developing ooecium). Its proximal edge is fl anked by a narrow
non- calcifi ed area.
On the inner surface of the ooecium, the medial suture
ends as a closed horizontal slit, more or less as in the cribrilinids Puellina , Figularia and Corbulipora (see Sect. 2.3.2 )
though somewhat different in shape. The adjoining lateral
surfaces of the ooecial lobes merge to form a two-layered longitudinal septum corresponding to the outer and inner medial
suture. As in Figularia , the ooecial coelomic cavity is represented by the lumen of each lobe communicating with each
other underneath the membranous wall of the non-calcifi ed
area on the proximal edge of the ooecium. The paired lumina
of the ooecium also communicate with the visceral coelom of
the parent zooid via two symmetric communication pores
situated directly below the ooecial lobes (Fig. 2.24 ). In
younger zooids they appear as non-parallel slits but later
transform into oval pores. Judging from the volume of the
ooecial coeloms and the size of the pores, the latter were open
in life, potentially allowing circulation of coelomic fl uid. It is
possible, however, that these pores later become plugged by
non- specialized epithelial cells (Ostrovsky et al. 2009a ).
The bases of the ooecial halves are rather narrow (in this
regard resembling the ovicells of extinct Wilbertopora , see
above). As the bases are formed, the lobes become broader.
Their lower edge grows proximally, fi rst adjoining the proximal gymnocyst of the distal zooid and then overgrowing the
lateral wall of the maternal zooid (see also Gordon ( 1986 , pl.
6A)). As in Wilbertopora , a suture remains between the
lower surface of the ooecial lobes and the zooidal surface.
Only about half the ovicell fl oor is represented by the
calcifi ed wall. The remaining half is formed by the thin noncalcifi ed distal wall of the maternal autozooid (Figs. 2.7a (F)
and 2.24 ). Its upper part forms the ooecial vesicle, the wall of
which has a thickened, sclerite-like, zone of cuticle. The
internal muscle bundles of the vesicle, inserting on its middle
and lower wall, effect opening of the ovicell by contracting
the vesicle. At their opposite ends, these bundles attach compactly to the basal wall of the maternal autozooid (Ostrovsky
et al. 2009a ).
2.3.1.6 Immersed Ovicells
Compared to Valdemunitella lata , the incubation chamber
of the immersed ovicell in Crassimarginatella sp. lies
completely in the distal part of the maternal autozooid
(Figs. 2.7b (B) and 2.25A ). The vestigial ooecium, slightly
protruding above the colony surface, is formed by the distal
autozooid (type 1, category A). It is represented by two
thick walls, the outer ectooecium and inner entooecium,
which fuse because of strong calcifi cation. Initially, the
coelom of the ooecium is a slit-like lumen lined with epithelial cells and communicating with the parent coelom via
an arched slit. Later, because of increased calcifi cation, the
ooecial coelom is reduced to a crescentic pit at the proximal
edge of the ooecium and the narrow canal that connects the
pit with the visceral coelom. The arched communication slit
becomes a closed groove with several pores or a single pore
at the bottom. In some old ooecia the communication canal
is completely closed and the pores at both ends are also not
retained.
The brood sac is a deep invagination of the distal wall of the
maternal autozooid (Figs. 2.7b (B) and 2.25A ). Distally, the
wall of the brood sac is attached to the transverse wall at
the base of the ooecium, whereas proximally it forms a kind of
ooecial vesicle overlapping the embryo from above. It was not
found to contain either a sclerite or specialized musculature,
and yet it closes the entrance to the brood cavity in the same
manner as an actual ooecial vesicle. Several muscle bundles
are attached to the sac wall in its proximal part, their opposite
ends being attached to the basal wall of the maternal autozooid.
They appear to extend the brood chamber during oviposition
and larval release. Immersed ovicells are also characteristic of
the calloporid genera Aplousina and Cranosina and the related
family Antroporidae (Ostrovsky et al. 2009a ).
2.3.1.7 Internal Brood Sac with Vestigial
Ooecium in Cauloramphus
In the genus Cauloramphus , all components of the brood
chamber are formed solely at the expense of the maternal
autozooid (type 2) (Ostrovsky 2008b ; Ostrovsky et al. 2007 ,
2009a ). The vestigial kenozooidal ooecium is budded at the
distal rim of the maternal autozooid, while its base merges
with the upper part of the distal wall of this zooid
(Figs. 2.6b (E), 2.7b (C), and 2.25B ). The ooecial cavity communicates with the visceral coelom via 1–3 communication
pores with pore-cell complexes (Fig. 2.25B ). The outer wall
of the ooecium (ectooecium) is uncalcifi ed except for its base
as a consequence of which, in cleaned specimens, it is mostly
entooecium that is visible, appearing as a prominent cap in
some species, while in Cauloramphus spinifer it appears as a
small plate with an arched outline. The ooecial cavity is a
deep groove. In older zooids, its lower part is partly reduced
by wall calcifi cation. This results in the formation of 1–3 coelomic canals, each leading to a communication pore. These
canals are connected with each other only in the upper part of
the ooecium, under the membranous area of the ectooecium.
The lumina of these canals are partly fi lled with loose epithelial
2 Cheilostome Brood Chambers: Structure, Formation, Evolution