161
strated by thin section in Arctonula arctica (Ostrovsky,
unpublished data) but the remainder of these genera have
not been studied anatomically.
The Microporidae contains genera with well-developed
ooecia ( Micropora , Mollia , Apiophragma ), vestigial ooecia
( Rosseliana ) and no ooecia ( Calpensia , Ogivalia , Microporina )
(Prenant and Bobin 1966 ; Hayward and Ryland 1998 ).
The same is true of the Umbonulidae; most genera have
hyperstomial or prominent ovicells, Desmacystis has
immersed ovicells with vestigial ooecia and Oshurkovia has
no ovicells at all (Hastings 1944 , 1964 ; Eggleston 1972 ;
Gordon and Grischenko 1994 ; Grischenko and Mawatari
2005 ). Recent Onychocellidae have vestigial ooecia. For
instance, Cook ( 1973 ) reported brooding in internal brood
sacs of Smittipora levinseni , in which a small ooecium is present (see Levinsen 1909 , pl. 24, fi g. 10). At the same time, some
onychocellids from the Cretaceous have well- developed
ooecia (Voigt 1989 ; Ostrovsky, unpublished data ).
Varying degrees of reduction of the ooecium and immersion of the brood cavity can be found in the Urceoliporidae.
Endozooidal and immersed ovicells are also present in species of Cheiloporinidae, Sclerodomidae, Metrarabdotosidae,
Myriaporidae and Porinidae. Remarkably, the cheiloporinid
Cheiloporina haddoni is strikingly similar to the calloporid
Crassimarginatella sp. in the mutual arrangement of the
brood-chamber components, whereas the brooding structures of Reciprocus regalis (Urceoliporidae) are very similar
to those in Beania bilaminata (Beaniidae) (Ostrovsky,
unpublished data). Thus, phylogenetically distant species
have convergently evolved extremely similar structures for
embryo incubation.
Within the family Cribrilinidae, fossil Leptocheilopora
(Fig. 2.26 ) and Recent Corbulipora , Euthyroides and some
Puellina (Fig. 2.27A ) have hyperstomial ovicells, whereas
subimmersed and endozooidal ovicells are also found in
Puellina (Figs. 2.7a (I), 2.27B–E , and 2.28 ), and endozooidal
in Figularia and Cribrilina (Ostrovsky, unpublished data).
The conclusion that a trend towards immersion of the brood
cavity is widespread in this group also emerges from an analysis of descriptions of various fossil cribrimorphs (see Lang
1916 , 1921 , 1922 ; Larwood 1962 ). Cribrimorph bryozoans
with subimmersed and endozooidal ovicells were common
as early as the Cretaceous. As in other groups, this trend was
accompanied by reduction of the ooecium. In Recent
Cribralaria austrinsulensis (Gordon 1989a ), Cribrilina dispersa and C . simplex (see Florence et al. 2007 ), ooecia seem
to be completely lacking. Ovicells are also unknown in
Jullienula . Accordingly, cribrimorphs also possesses the
whole range of brood structures from hyperstomial ovicells
to internal brood sacs. Lang ( 1921 ) cited cribrimorphs from
the Upper Cretaceous with endozooidal ovicells, the fi rst of
them appearing as early as the Cenomanian ( Calpidopora ).
The transitional series from hyperstomial to endozooidal
ovicells in Late Cretaceous Onychocellidae was described
by Voigt ( 1991 ). Thus, this trend in brood-chamber evolution
was expressed in the earliest cribrimorphs and onychocellids, which are among most ancient clades of brooding
cheilostomes.
The same situation obtains in the Chaperiidae, showing the
range from hyperstomial and prominent ( Chaperiopsis ,
Notocoryne , Larnacicus , Icelozoon , Exallozoon , Pyrichaperia ,
Exostesia ) to subimmersed ( Clipeochaperia ) to endozooidal
( Patsyella ) (Gordon 1982 , 1992 ). Species Chaperia have no
ovicells and brood embryos internally, as was recorded in
C . granulosa (Gordon and Mawatari 1992 ).
Levinsen ( 1909 ) remarked quite correctly that endozooidal ovicells are found in different families. On the basis of
this observation, however, he suggested that this type of
brood chamber structure was “old” (primitive) and “common” and subject to later substitution by other types.
A similar opinion was expressed by Harmer ( 1926 ) (see
above). My data indicate the contrary. Though the trend
towards immersion of the brood cavity manifested itself
early in the evolutionary history of fl ustrines, their fi rst ovicells were hyperstomial.
Thus, immersion of the brood cavity and reduction of the
ooecium are interrelated trends in the evolution of cheilostome brooding structures. The deeper the brood cavity lies
in the zooid, the less it protrudes and the smaller the ooecium. If ovicell immersion is achieved by overgrowth of a
layer of secondary calcifi cation, reduction of the ooecium
does not occur.
It should be noted that protection of the brood chamber
may be achieved not only by ovicell immersion. Additional
protective structures may also evolve. For instance, in
Isoschizoporella tricuspis and Petralia undata , ovicells are
formed in groups associated with spinose avicularia taller
than the ovicells (Ostrovsky, unpublished data).
2.4.8.5 Evolution of Internal Brood Sacs
The above examples show that the evolutionary trend
expressed in the immersion of the brood cavity into the colony is manifested in many taxa. This phenomenon has been
noted in at least 41 families (Ostrovsky et al. 2009b ; see also
Table 2.1 ). Thus, a quarter of the known cheilostome families, belonging to several superfamilies, include species with
different expressions of this trend. Half of these families
have species with internal brood sacs and no ooecia, and in
most such families species with ovicells also occur. These
facts give evidence that the transition from ovicells to internal brood sacs occurred repeatedly in cheilostomes
(Ostrovsky et al. 2006 , 2007 , 2009b ).
2.4 Evolution of Brood Chambers in Cheilostomata
strated by thin section in Arctonula arctica (Ostrovsky,
unpublished data) but the remainder of these genera have
not been studied anatomically.
The Microporidae contains genera with well-developed
ooecia ( Micropora , Mollia , Apiophragma ), vestigial ooecia
( Rosseliana ) and no ooecia ( Calpensia , Ogivalia , Microporina )
(Prenant and Bobin 1966 ; Hayward and Ryland 1998 ).
The same is true of the Umbonulidae; most genera have
hyperstomial or prominent ovicells, Desmacystis has
immersed ovicells with vestigial ooecia and Oshurkovia has
no ovicells at all (Hastings 1944 , 1964 ; Eggleston 1972 ;
Gordon and Grischenko 1994 ; Grischenko and Mawatari
2005 ). Recent Onychocellidae have vestigial ooecia. For
instance, Cook ( 1973 ) reported brooding in internal brood
sacs of Smittipora levinseni , in which a small ooecium is present (see Levinsen 1909 , pl. 24, fi g. 10). At the same time, some
onychocellids from the Cretaceous have well- developed
ooecia (Voigt 1989 ; Ostrovsky, unpublished data ).
Varying degrees of reduction of the ooecium and immersion of the brood cavity can be found in the Urceoliporidae.
Endozooidal and immersed ovicells are also present in species of Cheiloporinidae, Sclerodomidae, Metrarabdotosidae,
Myriaporidae and Porinidae. Remarkably, the cheiloporinid
Cheiloporina haddoni is strikingly similar to the calloporid
Crassimarginatella sp. in the mutual arrangement of the
brood-chamber components, whereas the brooding structures of Reciprocus regalis (Urceoliporidae) are very similar
to those in Beania bilaminata (Beaniidae) (Ostrovsky,
unpublished data). Thus, phylogenetically distant species
have convergently evolved extremely similar structures for
embryo incubation.
Within the family Cribrilinidae, fossil Leptocheilopora
(Fig. 2.26 ) and Recent Corbulipora , Euthyroides and some
Puellina (Fig. 2.27A ) have hyperstomial ovicells, whereas
subimmersed and endozooidal ovicells are also found in
Puellina (Figs. 2.7a (I), 2.27B–E , and 2.28 ), and endozooidal
in Figularia and Cribrilina (Ostrovsky, unpublished data).
The conclusion that a trend towards immersion of the brood
cavity is widespread in this group also emerges from an analysis of descriptions of various fossil cribrimorphs (see Lang
1916 , 1921 , 1922 ; Larwood 1962 ). Cribrimorph bryozoans
with subimmersed and endozooidal ovicells were common
as early as the Cretaceous. As in other groups, this trend was
accompanied by reduction of the ooecium. In Recent
Cribralaria austrinsulensis (Gordon 1989a ), Cribrilina dispersa and C . simplex (see Florence et al. 2007 ), ooecia seem
to be completely lacking. Ovicells are also unknown in
Jullienula . Accordingly, cribrimorphs also possesses the
whole range of brood structures from hyperstomial ovicells
to internal brood sacs. Lang ( 1921 ) cited cribrimorphs from
the Upper Cretaceous with endozooidal ovicells, the fi rst of
them appearing as early as the Cenomanian ( Calpidopora ).
The transitional series from hyperstomial to endozooidal
ovicells in Late Cretaceous Onychocellidae was described
by Voigt ( 1991 ). Thus, this trend in brood-chamber evolution
was expressed in the earliest cribrimorphs and onychocellids, which are among most ancient clades of brooding
cheilostomes.
The same situation obtains in the Chaperiidae, showing the
range from hyperstomial and prominent ( Chaperiopsis ,
Notocoryne , Larnacicus , Icelozoon , Exallozoon , Pyrichaperia ,
Exostesia ) to subimmersed ( Clipeochaperia ) to endozooidal
( Patsyella ) (Gordon 1982 , 1992 ). Species Chaperia have no
ovicells and brood embryos internally, as was recorded in
C . granulosa (Gordon and Mawatari 1992 ).
Levinsen ( 1909 ) remarked quite correctly that endozooidal ovicells are found in different families. On the basis of
this observation, however, he suggested that this type of
brood chamber structure was “old” (primitive) and “common” and subject to later substitution by other types.
A similar opinion was expressed by Harmer ( 1926 ) (see
above). My data indicate the contrary. Though the trend
towards immersion of the brood cavity manifested itself
early in the evolutionary history of fl ustrines, their fi rst ovicells were hyperstomial.
Thus, immersion of the brood cavity and reduction of the
ooecium are interrelated trends in the evolution of cheilostome brooding structures. The deeper the brood cavity lies
in the zooid, the less it protrudes and the smaller the ooecium. If ovicell immersion is achieved by overgrowth of a
layer of secondary calcifi cation, reduction of the ooecium
does not occur.
It should be noted that protection of the brood chamber
may be achieved not only by ovicell immersion. Additional
protective structures may also evolve. For instance, in
Isoschizoporella tricuspis and Petralia undata , ovicells are
formed in groups associated with spinose avicularia taller
than the ovicells (Ostrovsky, unpublished data).
2.4.8.5 Evolution of Internal Brood Sacs
The above examples show that the evolutionary trend
expressed in the immersion of the brood cavity into the colony is manifested in many taxa. This phenomenon has been
noted in at least 41 families (Ostrovsky et al. 2009b ; see also
Table 2.1 ). Thus, a quarter of the known cheilostome families, belonging to several superfamilies, include species with
different expressions of this trend. Half of these families
have species with internal brood sacs and no ooecia, and in
most such families species with ovicells also occur. These
facts give evidence that the transition from ovicells to internal brood sacs occurred repeatedly in cheilostomes
(Ostrovsky et al. 2006 , 2007 , 2009b ).
2.4 Evolution of Brood Chambers in Cheilostomata