123
Since calcifi cation of the incipient entooecium starts from
the upper margin of the transverse wall between the maternal
(proximal) zooid and the distal bud (or zooid), such that
the wall and entooecium are continuous, a further idea for
ooecial formation was suggested – that the entooecium
is derived from the maternal zooid and the ectooecium is
derived from the daughter zooid. This idea was fi rst mentioned
by Levinsen ( 1902 , p. 13), who wrote that “it is obvious
that the inner layer (the endoooecium) can be regarded as a
continuation of the distal [transverse] wall while the outer
layer (the ectoooecium) is formed from the front wall of the
distal zooecium”. Following the papers of Soule ( 1973 ) and
Harmelin ( 1973a ), this point of view reappeared in the literature as a compromise between the two earlier confl icting
opinions (cf. Cook 1977a , 1979 , 1985 ; Ryland 1979 , 1982 ;
Humphries 1979 ; Morris 1980 ; Cook and Chimonides
1981a ; Wass and Banta 1981 ; Ristedt 1985 ). For instance,
Harmelin ( 1973a ) interpreted ovicell formation in the calloporid Corbulella maderensis (as Crassimarginatella ) and
Cook ( 1979 ) in Doryporella alcicornis and Scrupocellaria
(Candidae) in this way. However, their morphological data
clearly show that all these authors described ooecia
formed by the daughter zooid and that the ooecial fold
should be considered in its entirety (Ostrovsky 1998 ; see
also Nielsen 1981 ).
Cook ( 1979 ) and Cook and Hayward ( 1983 ) outlined different variants of brood-chamber formation in Cheilostomata,
including that in several Lekythoporidae, in which zooids
have a distinctive orientation. Judging from their generalized
schematic for the family, they depicted the ooecium as
formed by the maternal autozooid, although polypide orientation shows that the ooecium obviously originated at the
expense of the distal zooid in an ancestral form.
An important landmark was the paper of Bishop and
Househam ( 1987 ), who described three categories of ovicells
[ooecia] “based on the timing of production of the ovicell in
relation to the budding of the maternal autozooid and of the
zooid distal to it” in the genus Puellina (Cribrilinidae). The
ovicell “is a proximal component of the distal zooid” in category A, and “of the kenozooid … distal to the maternal autozooid” in category B. “The ovicell appears to be a distal
component of the maternal zooid” in category C (Bishop and
Househam 1987 , p. 4). Two years previously, Ristedt ( 1985 )
illustrated the same three ovicell categories in Puellina
harmeri (as Cribrilaria ). Ostrovsky ( 1998 ) discussed these
fi ndings in the context of ooecium formation from the maternal zooid in confamilial Cribrilina annulata . Further analysis
of the literature and my own data led me to recognize two
main ovicell types in Cheilostomata, assigning ooecia in categories A and B of Bishop and Househam ( 1987 ) to one type
and category C to a second (Ostrovsky 1998 ; see also below).
However, since Callopora dumerilii has not been
restudied, Silén’s ( 1944 , 1945 ) statements that ooecia are
formed by the maternal autozooid in it, Scrupocellaria
scabra and other cheilostomes, could be neither refuted nor
ignored. I therefore investigated ovicell structure (anatomy
and external morphology) and development in C . dumerilii
and C . lineata (type species of Callopora ), with the aim of
resolving this long-standing controversy (Ostrovsky and
Schäfer 2003 ; Ostrovsky et al. 2003 ). It was confi rmed that
ooecia were formed by daughter zooids in both species. Early
stages of ovicellogenesis in C . lineata were studied, and no
knobs or any other outgrowths were found. An analysis of
text-fi gure 18 in Silén ( 1944 ) (representing a longitudinal
section of the ovicell in Scrupocellaria scabra ) (Fig. 2.4 )
and the accompanying description showed that he could not
have discovered any communication between the ooecial
fold and the distal zooid because of strong shrinkage in
alcohol-fi xed specimens. Studying three other species,
Silén ( 1945 ) did not make sections and referred to the misinterpreted structure of Scrupocellaria. Interestingly, Silén
himself explained the difference between his and Calvet’s
results for the same reason – he suggested that the latter
author worked with shrunken material. On the basis of these
and previous fi ndings, Silén’s ( 1944 , 1945 ) conclusions concerning ovicell structure were taken to be incorrect, and his
generalization was rejected. Since it has often been stressed
that both ooecial types exist among cheilostomes (Harmer
1902 ; Silén 1977 ; Ostrovsky 1998 , 2008b ; see also Ostrovsky
et al. 2009a ), sometimes in the same taxon, further research
was deemed necessary to verify what types are characteristic
of different taxa (Ostrovsky and Schäfer 2003 ).
A commonly expressed viewpoint in bryozoological
literature is that the ooecium is a heterozooid (Ström 1977 ;
Silén 1977 ; Ryland 1976 , 1979 , 1982 ; Cook 1979 ; Reed
1991 ) and that brood-chamber formation is thus an expression of the zooidal polymorphism that refl ects the high
level of colonial integration in bryozoans (Viskova 1992 ).
Woollacott and Zimmer ( 1972a ) found a calcifi ed septum
with a pore and a cell plug separating ooecial and visceral
coeloms in Bugula neritina (see also Calvet 1900 ), thereby
suggested that the ooecium might be a heterozooid (kenozooid). Ooecial lobes indeed appear to be kenozooids in
Scrupariidae and Alysidiidae (see below). In other cheilostomes, ooecia are kenozooids only if they bud from the
maternal autozooid (type II, see below) and there are specialized pore-cell complexes that plug communication pores.
As for cheilostomes with ooecia formed by the distal zooid
(type I), subsequent research has shown that they are not
kenozooids. Santagata and Banta ( 1996 ) described in detail
ovicell anatomy in Scrupocellaria ferox and showed that the
wide communication slit connecting the coeloms of the
distal zooid and the ooecium have no traces of a septum or
cell plug. Open communication pores have been found in
Callopora lineata (see Ostrovsky and Schäfer 2003 ). Even
when communication pores are completely plugged by
2.1 History of Studies of Cheilostome Brood Chambers
Since calcifi cation of the incipient entooecium starts from
the upper margin of the transverse wall between the maternal
(proximal) zooid and the distal bud (or zooid), such that
the wall and entooecium are continuous, a further idea for
ooecial formation was suggested – that the entooecium
is derived from the maternal zooid and the ectooecium is
derived from the daughter zooid. This idea was fi rst mentioned
by Levinsen ( 1902 , p. 13), who wrote that “it is obvious
that the inner layer (the endoooecium) can be regarded as a
continuation of the distal [transverse] wall while the outer
layer (the ectoooecium) is formed from the front wall of the
distal zooecium”. Following the papers of Soule ( 1973 ) and
Harmelin ( 1973a ), this point of view reappeared in the literature as a compromise between the two earlier confl icting
opinions (cf. Cook 1977a , 1979 , 1985 ; Ryland 1979 , 1982 ;
Humphries 1979 ; Morris 1980 ; Cook and Chimonides
1981a ; Wass and Banta 1981 ; Ristedt 1985 ). For instance,
Harmelin ( 1973a ) interpreted ovicell formation in the calloporid Corbulella maderensis (as Crassimarginatella ) and
Cook ( 1979 ) in Doryporella alcicornis and Scrupocellaria
(Candidae) in this way. However, their morphological data
clearly show that all these authors described ooecia
formed by the daughter zooid and that the ooecial fold
should be considered in its entirety (Ostrovsky 1998 ; see
also Nielsen 1981 ).
Cook ( 1979 ) and Cook and Hayward ( 1983 ) outlined different variants of brood-chamber formation in Cheilostomata,
including that in several Lekythoporidae, in which zooids
have a distinctive orientation. Judging from their generalized
schematic for the family, they depicted the ooecium as
formed by the maternal autozooid, although polypide orientation shows that the ooecium obviously originated at the
expense of the distal zooid in an ancestral form.
An important landmark was the paper of Bishop and
Househam ( 1987 ), who described three categories of ovicells
[ooecia] “based on the timing of production of the ovicell in
relation to the budding of the maternal autozooid and of the
zooid distal to it” in the genus Puellina (Cribrilinidae). The
ovicell “is a proximal component of the distal zooid” in category A, and “of the kenozooid … distal to the maternal autozooid” in category B. “The ovicell appears to be a distal
component of the maternal zooid” in category C (Bishop and
Househam 1987 , p. 4). Two years previously, Ristedt ( 1985 )
illustrated the same three ovicell categories in Puellina
harmeri (as Cribrilaria ). Ostrovsky ( 1998 ) discussed these
fi ndings in the context of ooecium formation from the maternal zooid in confamilial Cribrilina annulata . Further analysis
of the literature and my own data led me to recognize two
main ovicell types in Cheilostomata, assigning ooecia in categories A and B of Bishop and Househam ( 1987 ) to one type
and category C to a second (Ostrovsky 1998 ; see also below).
However, since Callopora dumerilii has not been
restudied, Silén’s ( 1944 , 1945 ) statements that ooecia are
formed by the maternal autozooid in it, Scrupocellaria
scabra and other cheilostomes, could be neither refuted nor
ignored. I therefore investigated ovicell structure (anatomy
and external morphology) and development in C . dumerilii
and C . lineata (type species of Callopora ), with the aim of
resolving this long-standing controversy (Ostrovsky and
Schäfer 2003 ; Ostrovsky et al. 2003 ). It was confi rmed that
ooecia were formed by daughter zooids in both species. Early
stages of ovicellogenesis in C . lineata were studied, and no
knobs or any other outgrowths were found. An analysis of
text-fi gure 18 in Silén ( 1944 ) (representing a longitudinal
section of the ovicell in Scrupocellaria scabra ) (Fig. 2.4 )
and the accompanying description showed that he could not
have discovered any communication between the ooecial
fold and the distal zooid because of strong shrinkage in
alcohol-fi xed specimens. Studying three other species,
Silén ( 1945 ) did not make sections and referred to the misinterpreted structure of Scrupocellaria. Interestingly, Silén
himself explained the difference between his and Calvet’s
results for the same reason – he suggested that the latter
author worked with shrunken material. On the basis of these
and previous fi ndings, Silén’s ( 1944 , 1945 ) conclusions concerning ovicell structure were taken to be incorrect, and his
generalization was rejected. Since it has often been stressed
that both ooecial types exist among cheilostomes (Harmer
1902 ; Silén 1977 ; Ostrovsky 1998 , 2008b ; see also Ostrovsky
et al. 2009a ), sometimes in the same taxon, further research
was deemed necessary to verify what types are characteristic
of different taxa (Ostrovsky and Schäfer 2003 ).
A commonly expressed viewpoint in bryozoological
literature is that the ooecium is a heterozooid (Ström 1977 ;
Silén 1977 ; Ryland 1976 , 1979 , 1982 ; Cook 1979 ; Reed
1991 ) and that brood-chamber formation is thus an expression of the zooidal polymorphism that refl ects the high
level of colonial integration in bryozoans (Viskova 1992 ).
Woollacott and Zimmer ( 1972a ) found a calcifi ed septum
with a pore and a cell plug separating ooecial and visceral
coeloms in Bugula neritina (see also Calvet 1900 ), thereby
suggested that the ooecium might be a heterozooid (kenozooid). Ooecial lobes indeed appear to be kenozooids in
Scrupariidae and Alysidiidae (see below). In other cheilostomes, ooecia are kenozooids only if they bud from the
maternal autozooid (type II, see below) and there are specialized pore-cell complexes that plug communication pores.
As for cheilostomes with ooecia formed by the distal zooid
(type I), subsequent research has shown that they are not
kenozooids. Santagata and Banta ( 1996 ) described in detail
ovicell anatomy in Scrupocellaria ferox and showed that the
wide communication slit connecting the coeloms of the
distal zooid and the ooecium have no traces of a septum or
cell plug. Open communication pores have been found in
Callopora lineata (see Ostrovsky and Schäfer 2003 ). Even
when communication pores are completely plugged by
2.1 History of Studies of Cheilostome Brood Chambers