138
the ooecial fold is in all the cases a continuation of the gymnocystal wall of the ooecium-producing zooid.
The vast majority of ooecia are complete. On the other
hand, in some calloporids ( Wilbertopora , Valdemunitella ,
Bryocalyx , Concertina , see above) and in many Cribrilinidae
ooecia have a median suture (Ostrovsky 1998 , 2002 , 2009 )
and may be called bilobate. Species of the cribrilinid genera
Figularia , Corbulipora , Euthyroides and Puellina have a
horizontal slit running perpendicular to the median suture on
the inner surface of the ooecium (Figs. 2.7a (I), 2.27C–E, G ,
and 2.28 ; note that similar slit exists in a costate ooecium of
the fossil Leptocheilopora magna , see Fig. 2.26C ). The coeloms of the ooecial lobes communicate with the visceral coelom of the distal zooid via two lateral communication slits
(Fig. 2.27G, H ). The same ooecial structure occurs in the
Bifaxariidae ( Diplonotos ), which is related to Cribrilinidae.
Communication slits later become communication pores,
which sometimes close because of ooecial-wall calcifi cation.
The median suture and independent lateral communication
slits indicates that the left and right halves of the ooecium
initially form independently, as two outgrowths. Later
they merge to form the hemispherical brood chamber typical of fossil and Recent calloporids like Wilbertopora and
Valdemunitella (see above). The early stages of ovicell-fl oor
calcifi cation in calloporids and cribrilinids with bilobate
ooecia, are represented by a non-paired plate (discussed in
Ostrovsky and Taylor 2005b ).
Cribrilina macropunctata , C . punctata and C . cryptooecium , on the other hand, have complete ooecia, lacking a
longitudinal suture. In these species the ooecial coelom
communicates with the zooidal coelom via a narrow arched
slit, retained from ovicellogenesis, just as in Recent calloporids. Likewise, early stages of ovicell-fl oor calcifi cation in
Recent cribrilinids and calloporids with complete ooecia are
represented by a paired plate (Levinsen 1909 , pl. 9, fi gs.
11a–c; Bishop 1994 , fi g. 17; Ostrovsky and Schäfer 2003 ;
Ostrovsky et al. 2003 , 2009a , unpublished data).
Cribrilina annulata has a kenozooidal ooecium. It appears
as a terminal cap on the distal wall of the maternal autozooid.
The space between the inner calcifi ed ooecial wall (entooecium) and non-calcifi ed distal wall of the maternal autozooid
is the brood chamber of the ovicell (Figs. 2.6b (A) and 2.29 ).
In this species, the ooecial coelom communicates with that of
the maternal autozooid via communication pores plugged by
specialized pore-cell complexes (Ostrovsky 1998 ). Ovicells
with an ‘intercalary’ kenozooidal ooecium in Eurystomella
(Eurystomellidae) have a similar structure (Fig. 2.6b (B))
(see also Levinsen 1909 , pl. 18, fi g. 14c).
Calloporiform ooecia form at the colony periphery
(Figs. 2.13B and 2.18 ). As noted above, the initial stage of
ovicell-fl oor calcifi cation may be a paired or a non-paired
plate (Figs. 2.11C, D , 2.13B , and 2.18A ). Paired plates occur in
the calloporid genera Callopora , Tegella , Crassimarginatella ,
Amphiblestrum and Parellisina (inter alia), the candid
genera Menipea , Scrupocellaria and Tricellaria , cribrilinid
genera Collarina and Cribrilina and the arachnopusiid
genus Arachnopusia , while non-paired plates occur in
the calloporid genera Wilbertopora and Valdemunitella ,
cribrilinid genera Corbulipora and Puellina , Euthyroididae
and Hippothoidae.
Most of the bryozoans listed above have hyperstomial,
prominent ovicells, while subimmersed, endozooidal or
immersed ones are less common, with different ovicell types
often found within one and the same family (for instance, in
Calloporidae), sometimes in the same genus ( Puellina ) or
even species ( Callopora lineata , Puellena radiata ) (compare
Figs. 2.13A and 2.15A ).
Endozooidal ovicells occur in species of Candidae
( Caberea ) (Fig. 2.30A ), Cribrilinidae ( Puellina , Figularia )
(Figs. 2.27B, C, E and 2.28 ), Eurystomellidae ( Selenariopsis )
(Fig. 2.7a (H)) and Catenicellidae ( Catenicella , Pterocella )
(Fig. 1.24A ). However, they are especially characteristic of
Flustridae (Figs. 1.17 , 2.7b (A), 2.31 , and 2.32 ). Most or all
of the brood cavity is immersed/enclosed in the distal zooid;
only in Flustra foliacea does the brood chamber of the ovicell go deeply into the cavity of the maternal autozooid (see
also Levinsen 1909 , pl. 24, fi gs. 6–8). The vestigial ooecium
is cap- or knob-shaped, with its base merging with the frontal
wall of the distal zooid. The ooecial coelom in this instance
communicates with the visceral coelom of the distal autozooid via a broad arched slit. The brood cavity and entooecium
appear to be formed as a result of invagination of the noncalcifi ed proximal part of the distal zooid. The entooecium
presumably increases in size by intercalary growth, while
the ectooecium grows little, if at all (Fig. 2.31D–H ) (see
Sect. 2.4.8 ). In empty ovicells of some species the ooecial
vesicle occupies nearly all or most of the brood cavity
(Figs. 1.17A , 2.7b (A), and 2.32A ), but it may also be only
weakly or moderately developed (Fig. 2.32B ).
Immersed ovicells are found in Antroporidae (Ostrovsky
et al. 2009a , b ) and Bugulopsis monotrypa (Candidae)
(Fig. 2.30B ). Some calloporids (Figs. 2.6b (E), 2.7b (C), and
2.46C ), some fl ustrids (Fig. 2.46A, B ) and Beaniidae (Fig. 1.22 )
have internal brood sacs with or without a vestigial ooecium.
Two types of ovicell structure are found in the Microporidae,
indicating an evolutionary connection between them – the
calloporiform type in Opaeophora and Micropora and the
escharelliform type (see below).
2.3.2.2 The Escharelliform Ooecium
This ooecial variant seems to have evolved independently
from the calloporiform type in the anascan families
Microporidae and Onychocellidae (Figs. 2.33A–C and 2.34 ),
the umbonulomorph families Romancheinidae, Lepraliellidae,
Sclerodomidae, and Metrarabdotosidae (Figs. 2.35A–D
and 2.36 ) and lepraliomorph families Phorioppniidae,
2 Cheilostome Brood Chambers: Structure, Formation, Evolution
the ooecial fold is in all the cases a continuation of the gymnocystal wall of the ooecium-producing zooid.
The vast majority of ooecia are complete. On the other
hand, in some calloporids ( Wilbertopora , Valdemunitella ,
Bryocalyx , Concertina , see above) and in many Cribrilinidae
ooecia have a median suture (Ostrovsky 1998 , 2002 , 2009 )
and may be called bilobate. Species of the cribrilinid genera
Figularia , Corbulipora , Euthyroides and Puellina have a
horizontal slit running perpendicular to the median suture on
the inner surface of the ooecium (Figs. 2.7a (I), 2.27C–E, G ,
and 2.28 ; note that similar slit exists in a costate ooecium of
the fossil Leptocheilopora magna , see Fig. 2.26C ). The coeloms of the ooecial lobes communicate with the visceral coelom of the distal zooid via two lateral communication slits
(Fig. 2.27G, H ). The same ooecial structure occurs in the
Bifaxariidae ( Diplonotos ), which is related to Cribrilinidae.
Communication slits later become communication pores,
which sometimes close because of ooecial-wall calcifi cation.
The median suture and independent lateral communication
slits indicates that the left and right halves of the ooecium
initially form independently, as two outgrowths. Later
they merge to form the hemispherical brood chamber typical of fossil and Recent calloporids like Wilbertopora and
Valdemunitella (see above). The early stages of ovicell-fl oor
calcifi cation in calloporids and cribrilinids with bilobate
ooecia, are represented by a non-paired plate (discussed in
Ostrovsky and Taylor 2005b ).
Cribrilina macropunctata , C . punctata and C . cryptooecium , on the other hand, have complete ooecia, lacking a
longitudinal suture. In these species the ooecial coelom
communicates with the zooidal coelom via a narrow arched
slit, retained from ovicellogenesis, just as in Recent calloporids. Likewise, early stages of ovicell-fl oor calcifi cation in
Recent cribrilinids and calloporids with complete ooecia are
represented by a paired plate (Levinsen 1909 , pl. 9, fi gs.
11a–c; Bishop 1994 , fi g. 17; Ostrovsky and Schäfer 2003 ;
Ostrovsky et al. 2003 , 2009a , unpublished data).
Cribrilina annulata has a kenozooidal ooecium. It appears
as a terminal cap on the distal wall of the maternal autozooid.
The space between the inner calcifi ed ooecial wall (entooecium) and non-calcifi ed distal wall of the maternal autozooid
is the brood chamber of the ovicell (Figs. 2.6b (A) and 2.29 ).
In this species, the ooecial coelom communicates with that of
the maternal autozooid via communication pores plugged by
specialized pore-cell complexes (Ostrovsky 1998 ). Ovicells
with an ‘intercalary’ kenozooidal ooecium in Eurystomella
(Eurystomellidae) have a similar structure (Fig. 2.6b (B))
(see also Levinsen 1909 , pl. 18, fi g. 14c).
Calloporiform ooecia form at the colony periphery
(Figs. 2.13B and 2.18 ). As noted above, the initial stage of
ovicell-fl oor calcifi cation may be a paired or a non-paired
plate (Figs. 2.11C, D , 2.13B , and 2.18A ). Paired plates occur in
the calloporid genera Callopora , Tegella , Crassimarginatella ,
Amphiblestrum and Parellisina (inter alia), the candid
genera Menipea , Scrupocellaria and Tricellaria , cribrilinid
genera Collarina and Cribrilina and the arachnopusiid
genus Arachnopusia , while non-paired plates occur in
the calloporid genera Wilbertopora and Valdemunitella ,
cribrilinid genera Corbulipora and Puellina , Euthyroididae
and Hippothoidae.
Most of the bryozoans listed above have hyperstomial,
prominent ovicells, while subimmersed, endozooidal or
immersed ones are less common, with different ovicell types
often found within one and the same family (for instance, in
Calloporidae), sometimes in the same genus ( Puellina ) or
even species ( Callopora lineata , Puellena radiata ) (compare
Figs. 2.13A and 2.15A ).
Endozooidal ovicells occur in species of Candidae
( Caberea ) (Fig. 2.30A ), Cribrilinidae ( Puellina , Figularia )
(Figs. 2.27B, C, E and 2.28 ), Eurystomellidae ( Selenariopsis )
(Fig. 2.7a (H)) and Catenicellidae ( Catenicella , Pterocella )
(Fig. 1.24A ). However, they are especially characteristic of
Flustridae (Figs. 1.17 , 2.7b (A), 2.31 , and 2.32 ). Most or all
of the brood cavity is immersed/enclosed in the distal zooid;
only in Flustra foliacea does the brood chamber of the ovicell go deeply into the cavity of the maternal autozooid (see
also Levinsen 1909 , pl. 24, fi gs. 6–8). The vestigial ooecium
is cap- or knob-shaped, with its base merging with the frontal
wall of the distal zooid. The ooecial coelom in this instance
communicates with the visceral coelom of the distal autozooid via a broad arched slit. The brood cavity and entooecium
appear to be formed as a result of invagination of the noncalcifi ed proximal part of the distal zooid. The entooecium
presumably increases in size by intercalary growth, while
the ectooecium grows little, if at all (Fig. 2.31D–H ) (see
Sect. 2.4.8 ). In empty ovicells of some species the ooecial
vesicle occupies nearly all or most of the brood cavity
(Figs. 1.17A , 2.7b (A), and 2.32A ), but it may also be only
weakly or moderately developed (Fig. 2.32B ).
Immersed ovicells are found in Antroporidae (Ostrovsky
et al. 2009a , b ) and Bugulopsis monotrypa (Candidae)
(Fig. 2.30B ). Some calloporids (Figs. 2.6b (E), 2.7b (C), and
2.46C ), some fl ustrids (Fig. 2.46A, B ) and Beaniidae (Fig. 1.22 )
have internal brood sacs with or without a vestigial ooecium.
Two types of ovicell structure are found in the Microporidae,
indicating an evolutionary connection between them – the
calloporiform type in Opaeophora and Micropora and the
escharelliform type (see below).
2.3.2.2 The Escharelliform Ooecium
This ooecial variant seems to have evolved independently
from the calloporiform type in the anascan families
Microporidae and Onychocellidae (Figs. 2.33A–C and 2.34 ),
the umbonulomorph families Romancheinidae, Lepraliellidae,
Sclerodomidae, and Metrarabdotosidae (Figs. 2.35A–D
and 2.36 ) and lepraliomorph families Phorioppniidae,
2 Cheilostome Brood Chambers: Structure, Formation, Evolution