133
zooid through a large oval opening (the former lateral slit)
(Fig. 2.12B, C ). The lobes start growing to form the vertical
walls of the ooecium (Fig. 2.12A ). Each lobe overgrows
the gymnocyst in a pro ximal direction towards the opening
of the maternal zooid (Fig. 2.11F–G ). For this reason, the
communication opening is always much smaller than the
total length of the basal part of the lobe. Thus, each lobe has
a relatively narrow base and a broad body. The frontal edges
of the lobes grow upwards and fuse along the midline of the
zooid to form a hemispherical hood-like ooecial roof, retaining the medial suture (Figs. 2.11H and 2.12D ) (Ostrovsky
and Taylor 2005b ).
2.3.1.3 Hyperstomial Ovicells
in Recent Calloporids
In Recent calloporids, ooecia are usually formed by the distal autozooid (type 1, category A) (Figs. 2.6a (A), 2.13 , 2.14 ,
2.15 , and 2.16 ), but in Callopora dumerilii and Corbulella
maderensis , the ooecium is also formed by the distal kenozooid (type 1, category B) (Figs. 2.6a (B) and 2.17C, D ) [similar cases are illustrated by Zabala and Maluquer ( 1988 , pl.
3C) and Gordon ( 1984) , pl. 1D]. Colonies of C . craticula in
which ooecia are formed by the distal autozooid were also
found to contain ovicells with ooecia formed by peripheral
“interzooidal” avicularia (type 1, category B) (Fig. 2.17A ) as
well as two instances of terminal ovicells with ooecia formed
by distal kenozooids lacking a prominent frontal part
(type 1, category B) (Fig. 2.17B ). In Concertina cultrata and
Bryocalyx cinnameus , hyperstomial ovicells are formed at
the periphery of the colony, in which growth ceases soon
after. The ooecium is formed by the distal kenozooid (type 1,
category B), which in C . cultrata can bud one more distal
autozooid (Figs. 2.6a (E) and 2.23 ) (Ostrovsky and Schäfer
2003 ; Ostrovsky et al. 2003 , 2009a ).
In most studied calloporids ovicells are acleithral, with
the opening closed by the ooecial vesicle (Figs. 2.6a (A, B, E),
2.7a (A, B), 2.14B , 2.15A, B , 2.16 , 2.22A , and 2.23 ). The
ooecial fold consists of inner (entooecial) and outer (ectooecial) walls with a narrow coelomic lumen between them. The
upper parts of ecto- and entooecium make up the ooecial
roof, merging at the edge of the ooecial fold surrounding the
ovicell opening. The ectooecium is more or less heavily calcifi ed in most species. Sometimes the only non-calcifi ed area
is an elongated arched or triangular membranous (cuticular)
window at the outer edge of the ectoooecium (Figs. 2.6a (A),
2.7a (C), 2.8B , 2.13A, B , 2.14A–C, E–F , 2.15A, B , 2.16 ,
2.17B, C , 2.19A, B , and 2.22 ). In C . craticula and Tegella
unicornis this window often has a prominent calcifi ed “collar” (Figs. 2.14C and 2.17B ). In contrast, in C . dumerilii the
ectooecium is non-calcifi ed except for a narrow basal part
(Figs. 2.6a (B), 2.13C , 2.14D , and 2.17D ). Another exception
is Bryocalyx cinnameus , in which most of the ectooecial wall
is also non- calcifi ed (Figs. 2.6a (E) and 2.23A ).
Entooecium is entirely calcifi ed. Its lower, moderately
concave part (ovicell fl oor) proximally joins the upper part of
the transverse wall between maternal and distal zooids and
the wall of the ooecial vesicle. The entooecial surface facing
the brood cavity is smooth, with concentric growth lines and
indistinct radial folds refl ecting its formation. The entooecial
surface facing the coelomic cavity of the ooecial fold is more
or less smooth (Figs. 2.13B and 2.14F ) or pustulose, its relief
resembling that of the zooidal cryptocyst (Figs. 2.13C and
2.14D ). In a single instance in both C . lineata and T . unicornis there was a medial groove at the edge of the ooecium
similar to that found in C . lineata by Prenant and Bobin
( 1966 ). Also, a short medial keel with a suture was found on
the inner ooecial surface in Corbulella maderensis . The keel
is on the inner (facing the brood cavity) side of the entooecium, disappearing more or less opposite the place where
there is a small outgrowth of ectooecium externally
(Fig. 2.22B ). In Concertina cultrata a medial suture runs
along the midline of the elongated ooecium with its pointed
apex (Ostrovsky et al. 2009a ).
The bilobate ooecium of Bryocalyx cinnameus also has
a longitudinal median suture and corresponding septum,
symmetrically dividing the ooecial roof into two parts.
The septum results from merging of the ooecial lobes. The
entooecium is entirely calcifi ed, whereas most of the ectooecium is membranous except for the narrow calcifi ed edges of
the ovicell opening and medial suture, and two fl at diagonal
ribs coming from these edges. (Fig. 2.23A ) (see also Cook
and Bock 2000 ). All of these calcifi ed elements form a
rigid framework of ectooecium. Two large oral spines surround the ovicell opening from above. The bases of the ooecial lobes fuse into a common unpaired base, while the
coeloms of the lobes communicate directly with the cavity of
the distal kenozooid. The latter in turn communicates with
the visceral coelom of the maternal autozooid via a few
groups of pores in the intervening transverse wall
(Fig. 2.23A ), plugged by pore-cell complexes typical of
cheilostomes (Fig. 2.15C ) (Ostrovsky et al. 2009a ).
The ooecial coelom is lined with fl at epidermal and peritoneal cells (with projections that sometimes stretch across
the lumen) and communicates with the cavity of the distal
zooid via its communication pore (Figs. 2.15A, B , 2.16 ,
2.21 , and 2.22A ) in the left or, more rarely, the right “corner” of the ooecial base. There are sometimes 2–3 such pores
(Fig. 2.21D ), representing the remnants of the arched communication slit (Fig. 2.20 ) that forms when the ooecium is
formed. In young zooids this slit, though closed, remains
plainly visible as an arched suture (Fig. 2.21A ); in older
zooids a shallow groove is retained (Fig. 2.21B, C ) (Ostrovsky
and Schäfer 2003 ).
Thickening of ooecial walls, characteristic of most calloporids, results in progressive narrowing of the ooecial
coelom. In developing and young fully formed ovicells it
2.3 Structure and Development of Brood Chambers in Cheilostomata
zooid through a large oval opening (the former lateral slit)
(Fig. 2.12B, C ). The lobes start growing to form the vertical
walls of the ooecium (Fig. 2.12A ). Each lobe overgrows
the gymnocyst in a pro ximal direction towards the opening
of the maternal zooid (Fig. 2.11F–G ). For this reason, the
communication opening is always much smaller than the
total length of the basal part of the lobe. Thus, each lobe has
a relatively narrow base and a broad body. The frontal edges
of the lobes grow upwards and fuse along the midline of the
zooid to form a hemispherical hood-like ooecial roof, retaining the medial suture (Figs. 2.11H and 2.12D ) (Ostrovsky
and Taylor 2005b ).
2.3.1.3 Hyperstomial Ovicells
in Recent Calloporids
In Recent calloporids, ooecia are usually formed by the distal autozooid (type 1, category A) (Figs. 2.6a (A), 2.13 , 2.14 ,
2.15 , and 2.16 ), but in Callopora dumerilii and Corbulella
maderensis , the ooecium is also formed by the distal kenozooid (type 1, category B) (Figs. 2.6a (B) and 2.17C, D ) [similar cases are illustrated by Zabala and Maluquer ( 1988 , pl.
3C) and Gordon ( 1984) , pl. 1D]. Colonies of C . craticula in
which ooecia are formed by the distal autozooid were also
found to contain ovicells with ooecia formed by peripheral
“interzooidal” avicularia (type 1, category B) (Fig. 2.17A ) as
well as two instances of terminal ovicells with ooecia formed
by distal kenozooids lacking a prominent frontal part
(type 1, category B) (Fig. 2.17B ). In Concertina cultrata and
Bryocalyx cinnameus , hyperstomial ovicells are formed at
the periphery of the colony, in which growth ceases soon
after. The ooecium is formed by the distal kenozooid (type 1,
category B), which in C . cultrata can bud one more distal
autozooid (Figs. 2.6a (E) and 2.23 ) (Ostrovsky and Schäfer
2003 ; Ostrovsky et al. 2003 , 2009a ).
In most studied calloporids ovicells are acleithral, with
the opening closed by the ooecial vesicle (Figs. 2.6a (A, B, E),
2.7a (A, B), 2.14B , 2.15A, B , 2.16 , 2.22A , and 2.23 ). The
ooecial fold consists of inner (entooecial) and outer (ectooecial) walls with a narrow coelomic lumen between them. The
upper parts of ecto- and entooecium make up the ooecial
roof, merging at the edge of the ooecial fold surrounding the
ovicell opening. The ectooecium is more or less heavily calcifi ed in most species. Sometimes the only non-calcifi ed area
is an elongated arched or triangular membranous (cuticular)
window at the outer edge of the ectoooecium (Figs. 2.6a (A),
2.7a (C), 2.8B , 2.13A, B , 2.14A–C, E–F , 2.15A, B , 2.16 ,
2.17B, C , 2.19A, B , and 2.22 ). In C . craticula and Tegella
unicornis this window often has a prominent calcifi ed “collar” (Figs. 2.14C and 2.17B ). In contrast, in C . dumerilii the
ectooecium is non-calcifi ed except for a narrow basal part
(Figs. 2.6a (B), 2.13C , 2.14D , and 2.17D ). Another exception
is Bryocalyx cinnameus , in which most of the ectooecial wall
is also non- calcifi ed (Figs. 2.6a (E) and 2.23A ).
Entooecium is entirely calcifi ed. Its lower, moderately
concave part (ovicell fl oor) proximally joins the upper part of
the transverse wall between maternal and distal zooids and
the wall of the ooecial vesicle. The entooecial surface facing
the brood cavity is smooth, with concentric growth lines and
indistinct radial folds refl ecting its formation. The entooecial
surface facing the coelomic cavity of the ooecial fold is more
or less smooth (Figs. 2.13B and 2.14F ) or pustulose, its relief
resembling that of the zooidal cryptocyst (Figs. 2.13C and
2.14D ). In a single instance in both C . lineata and T . unicornis there was a medial groove at the edge of the ooecium
similar to that found in C . lineata by Prenant and Bobin
( 1966 ). Also, a short medial keel with a suture was found on
the inner ooecial surface in Corbulella maderensis . The keel
is on the inner (facing the brood cavity) side of the entooecium, disappearing more or less opposite the place where
there is a small outgrowth of ectooecium externally
(Fig. 2.22B ). In Concertina cultrata a medial suture runs
along the midline of the elongated ooecium with its pointed
apex (Ostrovsky et al. 2009a ).
The bilobate ooecium of Bryocalyx cinnameus also has
a longitudinal median suture and corresponding septum,
symmetrically dividing the ooecial roof into two parts.
The septum results from merging of the ooecial lobes. The
entooecium is entirely calcifi ed, whereas most of the ectooecium is membranous except for the narrow calcifi ed edges of
the ovicell opening and medial suture, and two fl at diagonal
ribs coming from these edges. (Fig. 2.23A ) (see also Cook
and Bock 2000 ). All of these calcifi ed elements form a
rigid framework of ectooecium. Two large oral spines surround the ovicell opening from above. The bases of the ooecial lobes fuse into a common unpaired base, while the
coeloms of the lobes communicate directly with the cavity of
the distal kenozooid. The latter in turn communicates with
the visceral coelom of the maternal autozooid via a few
groups of pores in the intervening transverse wall
(Fig. 2.23A ), plugged by pore-cell complexes typical of
cheilostomes (Fig. 2.15C ) (Ostrovsky et al. 2009a ).
The ooecial coelom is lined with fl at epidermal and peritoneal cells (with projections that sometimes stretch across
the lumen) and communicates with the cavity of the distal
zooid via its communication pore (Figs. 2.15A, B , 2.16 ,
2.21 , and 2.22A ) in the left or, more rarely, the right “corner” of the ooecial base. There are sometimes 2–3 such pores
(Fig. 2.21D ), representing the remnants of the arched communication slit (Fig. 2.20 ) that forms when the ooecium is
formed. In young zooids this slit, though closed, remains
plainly visible as an arched suture (Fig. 2.21A ); in older
zooids a shallow groove is retained (Fig. 2.21B, C ) (Ostrovsky
and Schäfer 2003 ).
Thickening of ooecial walls, characteristic of most calloporids, results in progressive narrowing of the ooecial
coelom. In developing and young fully formed ovicells it
2.3 Structure and Development of Brood Chambers in Cheilostomata