125
adjoining zooidal mural spines, the frontal wall (including
frontal membrane), and the epistegal space between them
(see Ostrovsky and Taylor 2005a ) (Figs. 2.50 , 2.51 , and
2.59A, B ), all of these chambers are known as “ovicells”
(Figs. 1.17 , 1.18A, B , 1.19B–D , 1.20D–E , 1.25A , 1.27D ,
1.28C–D , 1.29B , 1.30A, B , 1.32A, B , 1.36 , 2.1 , 2.3 , 2.4 , 2.5 ,
2.6a, b (A–D, F), 2.7a, b (A, B, F), 2.8 , 2.9 , 2.10 , 2.11 , 2.12 ,
2.13 , 2.14 , 2.15 , 2.16 , 2.17 , 2.18 , 2.19 , 2.20 , 2.21 , 2.22 , 2.23 ,
2.24 , 2.25A , 2.26 , 2.27 , 2.28 , 2.29 , 2.30 , 2.31 , 2.32 , 2.33 ,
2.34 , 2.35 , 2.36 , 2.37 , 2.38 , 2.39 , 2.40 , 2.41 , 2.42 , 2.43 , 2.44 ,
2.45 , 2.48 , 2.49 , 2.54 , 2.55 , 2.56 , 2.57 , 2.58 , 2.59C–E , 2.60 ,
2.61 , 2.62 , 2.63 , 2.64 , and 2.65 ).
In general, each ovicell consists of a two-walled, completely
or partially calcifi ed protective ooecial fold (ooecium) with
an enclosed coelomic lumen, a non-calcifi ed part of the distal
wall of the maternal (egg-producing) autozooid that plugs the
ovicell opening, and the topologically exterior brood cavity
between them (see Fig. 1 in Introduction, Figs. 2.6 , 2.7 and
2.8 ) (Ryland 1976 ; Ostrovsky 2008a , b ). Among cheilostomes, ooecium size and shape vary from prominent and
hemispherical to vestigial and cap-like. The outer ooecial
wall is ectooecium; that surrounding the brood cavity,
entooecium. The lower concave part of the entooecium,
proximally continuous with the transverse wall of the zooid,
is the ovicell fl oor. The upper part of the ovicell capsule
(ooecium) is sometimes called a roof, whereas the sides are
vertical walls. Both include parts of the ento- and ectooecium. The ovicell opening is closed either by the operculum
of the zooidal aperture, or by a non-calcifi ed part of the distal wall of the maternal cystid, or both. Often this wall forms
an evagination called an ooecial (inner) vesicle. This vesicle
can be contracted by special muscle bands, thereby opening
the ovicell entrance. In some species, ovicells are permanently open (see below), and the maternal zooid does not
contribute to ovicell closure. Depending on the type of formation, the ooecial coelomic cavity communicates either
with the coelom of the daughter or maternal zooid through
communication pore(s). If the ooecium is formed by the
daughter zooid, these pores are often (but not always)
plugged by non-specialized epithelial cells, so that the
coeloms are not confl uent. If the ooecium is budded from
the maternal zooid, the communication pore(s) is plugged
by the pore-cell complex that is normally found in a septular
pore. In both cases, an ovicell is a complex structure (colonial organ), involving at least two zooids in its formation
(for original terms and additional schemes see Levinsen
1909 ; Harmer 1926 , 1957 ; Woollacott and Zimmer 1972a ;
Ryland 1968 , 1976 ; Ryland and Hayward 1977 ; Santagata
and Banta 1996 ; Hayward and Ryland 1979 , 1998 , 1999 ;
Ostrovsky 1998 , 2008a , b ; Ostrovsky and Schäfer 2003 ;
Ostrovsky et al. 2003 , 2009a ).
In many taxa, however, ooecial structure is more complex
than this. Levinsen ( 1902 , p. 14, 1909 ) was the fi rst to separate
“ooecia with a cryptocyst” from those without it (see also
Harmer 1957 ; Woollacott and Zimmer 1972a , for discussion).
A complex ovicell roof with a “cryptocystal matrix” was
recently discovered in some Macropora and Monoporella
species (Ostrovsky and Taylor 2005a ).
The terms “ovicell” and “ooecium” (refl ecting an early
supposition that the chamber contains an ovary) were introduced by Busk ( 1852 ) and Hincks ( 1873 ), and have been
effectively regarded as synonymous. However, as soon as
anatomical descriptions appeared (Vigelius 1884a , b , 1886 ;
Calvet 1900 ) it became clear that such synonymy is misleading. One problem is that the terms “ovicell” and “ooecium”
are generally applied to both the externally visible part of the
brood chamber and the entire structure. The most obvious
example is the often-used phrase “vestigial ovicell,” which is
terminologically nonsensical, since “vestigial” can apply
only to the protective fold (ooecium), whereas the actual
brood cavity is always capacious. An ovicell cannot be
vestigial. In another example, an immersed ovicell is typifi ed by a brood cavity that is situated below the colony
surface, whereas its ooecium is an external structure and
cannot be immersed. The same is true of endozooidal ovicells possessing an internal cavity for embryo incubation and
externally projecting ooecia. Interestingly, Busk ( 1884 ), who
introduced the term “ovicell”, in his famous description of
the collection of the “Challenger” expedition, used Hincks’s
term “ooecium”.
The terminological changes made by Ryland ( 1976 ) and
Reed ( 1991 ) refl ect the need to distinguish the entire brood
chamber from its parts, namely the protective hood (ooecium
or ooecial outfold), brood cavity, and closing device (either a
non-calcifi ed part of the distal wall of the maternal cystid or
the ooecial vesicle) (see also Silén 1945 ; Ryland and
Hayward 1977 ; Ryland 1979 ; Hayward and Ryland 1979 ).
This need refl ects the fact that the brood-chamber complex
in Cheilostomata is “usually produced by a collaboration
between the maternal zooid and the next distal [daughter]
zooid” (Reed 1991 , p. 149).
2.2.1 Ooecium Formation
This aspect of ovicell structure is particularly complex and
cannot be elucidated without recourse to anatomical study
or at least examining fractured or sectioned skeletons.
Analysis of the literature and my own anatomical studies
show that all ovicells can be classifi ed according to the
ooecium- producing zooid and the nature of the ooecium
itself. Two types of ooecium formation can be formally
defi ned (1st and 2nd types in Ostrovsky 1998 ). In “type 1”
the ooecium is formed either by the distal autozooid (“category A” of Bishop and Househam 1987 ), or by an avicularium or kenozooid (“category B”) with or without a distally
2.2 Classifi cation and Terminology
adjoining zooidal mural spines, the frontal wall (including
frontal membrane), and the epistegal space between them
(see Ostrovsky and Taylor 2005a ) (Figs. 2.50 , 2.51 , and
2.59A, B ), all of these chambers are known as “ovicells”
(Figs. 1.17 , 1.18A, B , 1.19B–D , 1.20D–E , 1.25A , 1.27D ,
1.28C–D , 1.29B , 1.30A, B , 1.32A, B , 1.36 , 2.1 , 2.3 , 2.4 , 2.5 ,
2.6a, b (A–D, F), 2.7a, b (A, B, F), 2.8 , 2.9 , 2.10 , 2.11 , 2.12 ,
2.13 , 2.14 , 2.15 , 2.16 , 2.17 , 2.18 , 2.19 , 2.20 , 2.21 , 2.22 , 2.23 ,
2.24 , 2.25A , 2.26 , 2.27 , 2.28 , 2.29 , 2.30 , 2.31 , 2.32 , 2.33 ,
2.34 , 2.35 , 2.36 , 2.37 , 2.38 , 2.39 , 2.40 , 2.41 , 2.42 , 2.43 , 2.44 ,
2.45 , 2.48 , 2.49 , 2.54 , 2.55 , 2.56 , 2.57 , 2.58 , 2.59C–E , 2.60 ,
2.61 , 2.62 , 2.63 , 2.64 , and 2.65 ).
In general, each ovicell consists of a two-walled, completely
or partially calcifi ed protective ooecial fold (ooecium) with
an enclosed coelomic lumen, a non-calcifi ed part of the distal
wall of the maternal (egg-producing) autozooid that plugs the
ovicell opening, and the topologically exterior brood cavity
between them (see Fig. 1 in Introduction, Figs. 2.6 , 2.7 and
2.8 ) (Ryland 1976 ; Ostrovsky 2008a , b ). Among cheilostomes, ooecium size and shape vary from prominent and
hemispherical to vestigial and cap-like. The outer ooecial
wall is ectooecium; that surrounding the brood cavity,
entooecium. The lower concave part of the entooecium,
proximally continuous with the transverse wall of the zooid,
is the ovicell fl oor. The upper part of the ovicell capsule
(ooecium) is sometimes called a roof, whereas the sides are
vertical walls. Both include parts of the ento- and ectooecium. The ovicell opening is closed either by the operculum
of the zooidal aperture, or by a non-calcifi ed part of the distal wall of the maternal cystid, or both. Often this wall forms
an evagination called an ooecial (inner) vesicle. This vesicle
can be contracted by special muscle bands, thereby opening
the ovicell entrance. In some species, ovicells are permanently open (see below), and the maternal zooid does not
contribute to ovicell closure. Depending on the type of formation, the ooecial coelomic cavity communicates either
with the coelom of the daughter or maternal zooid through
communication pore(s). If the ooecium is formed by the
daughter zooid, these pores are often (but not always)
plugged by non-specialized epithelial cells, so that the
coeloms are not confl uent. If the ooecium is budded from
the maternal zooid, the communication pore(s) is plugged
by the pore-cell complex that is normally found in a septular
pore. In both cases, an ovicell is a complex structure (colonial organ), involving at least two zooids in its formation
(for original terms and additional schemes see Levinsen
1909 ; Harmer 1926 , 1957 ; Woollacott and Zimmer 1972a ;
Ryland 1968 , 1976 ; Ryland and Hayward 1977 ; Santagata
and Banta 1996 ; Hayward and Ryland 1979 , 1998 , 1999 ;
Ostrovsky 1998 , 2008a , b ; Ostrovsky and Schäfer 2003 ;
Ostrovsky et al. 2003 , 2009a ).
In many taxa, however, ooecial structure is more complex
than this. Levinsen ( 1902 , p. 14, 1909 ) was the fi rst to separate
“ooecia with a cryptocyst” from those without it (see also
Harmer 1957 ; Woollacott and Zimmer 1972a , for discussion).
A complex ovicell roof with a “cryptocystal matrix” was
recently discovered in some Macropora and Monoporella
species (Ostrovsky and Taylor 2005a ).
The terms “ovicell” and “ooecium” (refl ecting an early
supposition that the chamber contains an ovary) were introduced by Busk ( 1852 ) and Hincks ( 1873 ), and have been
effectively regarded as synonymous. However, as soon as
anatomical descriptions appeared (Vigelius 1884a , b , 1886 ;
Calvet 1900 ) it became clear that such synonymy is misleading. One problem is that the terms “ovicell” and “ooecium”
are generally applied to both the externally visible part of the
brood chamber and the entire structure. The most obvious
example is the often-used phrase “vestigial ovicell,” which is
terminologically nonsensical, since “vestigial” can apply
only to the protective fold (ooecium), whereas the actual
brood cavity is always capacious. An ovicell cannot be
vestigial. In another example, an immersed ovicell is typifi ed by a brood cavity that is situated below the colony
surface, whereas its ooecium is an external structure and
cannot be immersed. The same is true of endozooidal ovicells possessing an internal cavity for embryo incubation and
externally projecting ooecia. Interestingly, Busk ( 1884 ), who
introduced the term “ovicell”, in his famous description of
the collection of the “Challenger” expedition, used Hincks’s
term “ooecium”.
The terminological changes made by Ryland ( 1976 ) and
Reed ( 1991 ) refl ect the need to distinguish the entire brood
chamber from its parts, namely the protective hood (ooecium
or ooecial outfold), brood cavity, and closing device (either a
non-calcifi ed part of the distal wall of the maternal cystid or
the ooecial vesicle) (see also Silén 1945 ; Ryland and
Hayward 1977 ; Ryland 1979 ; Hayward and Ryland 1979 ).
This need refl ects the fact that the brood-chamber complex
in Cheilostomata is “usually produced by a collaboration
between the maternal zooid and the next distal [daughter]
zooid” (Reed 1991 , p. 149).
2.2.1 Ooecium Formation
This aspect of ovicell structure is particularly complex and
cannot be elucidated without recourse to anatomical study
or at least examining fractured or sectioned skeletons.
Analysis of the literature and my own anatomical studies
show that all ovicells can be classifi ed according to the
ooecium- producing zooid and the nature of the ooecium
itself. Two types of ooecium formation can be formally
defi ned (1st and 2nd types in Ostrovsky 1998 ). In “type 1”
the ooecium is formed either by the distal autozooid (“category A” of Bishop and Househam 1987 ), or by an avicularium or kenozooid (“category B”) with or without a distally
2.2 Classifi cation and Terminology