141
postponed. Instead, there is an arched groove containing a
slit-like communication pore in the proximal part of the
incompletely formed frontal shield of a developing ooeciumproducing autozooid at the colony periphery. The groove is
covered by a cuticular wall, and its coelomic cavity is isolated
from the hypostegal coelom of the distal zooid by a narrow
arch of calcifi cation (the base of the provisional ectooecium);
the communication pore leads to the visceral coelom of the
distal bud. The entire structure (groove and pore) comprises
the base of the developmentally retarded provisional ooecial
fold. Thus, whereas base of the ooecium originates at the
colony periphery, the actual ooecial fold can be formed later
when the ooecium-producing zooid is no longer at the
periphery.
2.3.2.4 The Microporelliform Ooecium
This variant is found only in lepraliomorph ascophorans (e.g.
families Microporellidae, Pacifi cincolidae, Schizoporellidae,
Myriaporidae, Porinidae) (Figs. 2.43A–D , 2.44 , and 2.65C ;
see also fi g. 17 showing a schematic of ovicell anatomy.
Pacifi cincola insculpta (as ‘ Hippodiplosia ’) in Nielsen 1981 ).
The ooecium is again an outgrowth of the proximal part
of the frontal shield of the distal autozooid and consists of
two walls with a coelomic cavity between them (Figs. 2.43C, D ,
2.44 , and 2.65C ). The outer wall (ectooecium) is noncalcifi ed, being a continuation of the frontal wall of the distal
autozooid (as in the escharelliform ooecium). The calcifi ed
inner wall (entooecium) is connected with the proximal part
of the frontal shield of the distal zooid. The ovicell fl oor is
represented by a horizontal area of entooecium that is fused
with the calcifi ed proximal part of the distal frontal shield by
several crossbar-like ridges. A narrow coelomic space is
retained between the entooecium and the proximal part of
the frontal shield, communicating (as does the rest of the
ooecial coelom), with the hypostegal coelom of the distal
autozooid (Figs. 2.43C and 2.44 ). There are no pores, hence
no communication, between ooecial and visceral coeloms.
Ovicellogenesis proceeds at a considerable distance from
the colony periphery. It involves the formation of an arched
ooecial fold, accompanied by gradual calcifi cation of the
proximal part of the frontal shield of the distal zooid. The
provisional ovicell fl oor initially appears as an unpaired
semicircular plate extending from the transverse wall (see
also illustrations in Nielsen 1981 ; Mawatari et al. 1991 ;
Suwa and Mawatari 1998 ; Mawatari and Suwa 1998 ; Suwa
et al. 1998 ). Its calcifi cation overgrows the proximal hypostegal coelom and frontal shield of the underlying distal zooid,
fusing with its calcifi ed wall by means of protuberances or
crests of the wall (sometimes present only at the edge of the
ovicell fl oor) transforming to skeletal crossbars. The fully
developed fl at ovicell fl oor is skirted by a low ooecial fold
of the non-calcifi ed frontal wall of the distal zooid. This fold
grows vertically and then centripetally, accompanied by progressive thickening of the calcifi ed entooecium.
2.3.2.5 The Case of Fenestrulina
In species of Fenestrulina (Microporellidae), the fl oor of the
brood cavity comprises entooecium fused with the proximal
area of the frontal shield of the distal autozooid by means of
several (16–18) radial crossbars; spaces between them
describe an arch of pores around the entooecial base
(Figs. 2.1 , 2.8D , 2.43E, F , 2.45 , and 2.65B ). Between the
ovicell fl oor and the proximal part of the frontal shield, a narrow coelomic space is retained that communicates with the
ooecial coelom via the pores between the crossbars. The
entooecium is surrounded by a raised lip, with a narrow rim
of gymnocyst (Fig. 2.43E–F ), that represents the calcifi ed
base of the ectooecium and the site where its non-calcifi ed
part is attached to the frontal shield. Because of this lip, the
ooecial coelom is isolated from the hypostegal coelom of the
distal zooid. The narrow ooecial cavity communicates with
the visceral coelom of the distal autozooid via a central slitlike pore; it is arched and located near the transverse wall
between the maternal and distal zooids (Figs. 2.1 , 2.8D ,
2.45 , and 2.65B ; see also Nielsen 1981 , fi g. 18B).
The ooecium is formed as an arched fold in the proximal
part of peripheral zooid buds in which formation of the
frontal shield is underway (Nielsen 1981 , fi gs. 17–19). The
earliest stage of calcifi cation of the provisional ovicell fl oor
is an unpaired tongue-like plate initiated from the transverse
zooidal wall. Further growth of the ooecial fold resembles
that in the lepralielliform variant although a double disc is
not formed (see Fig. 2.40 and description above).
The lower lateral areas of calcifi cation of the ooecial fold
grow towards each other, together with the proximal areas of
the developing frontal shield. Fusion of these areas beneath
the provisional ovicell fl oor (horizontal part of the entooecium) and formation of the calcifi ed base of ectooecium
result in separation of the coelomic cavity of the growing
ooecial fold from the hypostegal coelom of the distal zooid
and in the formation of the proximal part of its frontal shield
with central communication in the form of a slit-like pore
(Figs. 2.1 , 2.8D , and 2.45 ; see also Nielsen 1981 , Figs.
1.17B , 1.18 ). Further, the frontal shield fuses with the ovicell
fl oor by means of radial crossbars.
Fusion of the horizontal area of the entooecium with the
frontal shield and the lack of a double disc are microporelliform, whereas isolation of the ooecial and hypostegal
coeloms, the presence of the communication pore and early
ovicellogenesis are lepralielliform. It should also be noted
that, judging from the description of Nielsen ( 1981 ), F . miramara (as F . malusii ) has cleithral ovicells. In contrast, Calvet
( 1900 , fi g. 21) depicted an acleithral ovicell in F . malusii
(as Microporella ).
2.3 Structure and Development of Brood Chambers in Cheilostomata
postponed. Instead, there is an arched groove containing a
slit-like communication pore in the proximal part of the
incompletely formed frontal shield of a developing ooeciumproducing autozooid at the colony periphery. The groove is
covered by a cuticular wall, and its coelomic cavity is isolated
from the hypostegal coelom of the distal zooid by a narrow
arch of calcifi cation (the base of the provisional ectooecium);
the communication pore leads to the visceral coelom of the
distal bud. The entire structure (groove and pore) comprises
the base of the developmentally retarded provisional ooecial
fold. Thus, whereas base of the ooecium originates at the
colony periphery, the actual ooecial fold can be formed later
when the ooecium-producing zooid is no longer at the
periphery.
2.3.2.4 The Microporelliform Ooecium
This variant is found only in lepraliomorph ascophorans (e.g.
families Microporellidae, Pacifi cincolidae, Schizoporellidae,
Myriaporidae, Porinidae) (Figs. 2.43A–D , 2.44 , and 2.65C ;
see also fi g. 17 showing a schematic of ovicell anatomy.
Pacifi cincola insculpta (as ‘ Hippodiplosia ’) in Nielsen 1981 ).
The ooecium is again an outgrowth of the proximal part
of the frontal shield of the distal autozooid and consists of
two walls with a coelomic cavity between them (Figs. 2.43C, D ,
2.44 , and 2.65C ). The outer wall (ectooecium) is noncalcifi ed, being a continuation of the frontal wall of the distal
autozooid (as in the escharelliform ooecium). The calcifi ed
inner wall (entooecium) is connected with the proximal part
of the frontal shield of the distal zooid. The ovicell fl oor is
represented by a horizontal area of entooecium that is fused
with the calcifi ed proximal part of the distal frontal shield by
several crossbar-like ridges. A narrow coelomic space is
retained between the entooecium and the proximal part of
the frontal shield, communicating (as does the rest of the
ooecial coelom), with the hypostegal coelom of the distal
autozooid (Figs. 2.43C and 2.44 ). There are no pores, hence
no communication, between ooecial and visceral coeloms.
Ovicellogenesis proceeds at a considerable distance from
the colony periphery. It involves the formation of an arched
ooecial fold, accompanied by gradual calcifi cation of the
proximal part of the frontal shield of the distal zooid. The
provisional ovicell fl oor initially appears as an unpaired
semicircular plate extending from the transverse wall (see
also illustrations in Nielsen 1981 ; Mawatari et al. 1991 ;
Suwa and Mawatari 1998 ; Mawatari and Suwa 1998 ; Suwa
et al. 1998 ). Its calcifi cation overgrows the proximal hypostegal coelom and frontal shield of the underlying distal zooid,
fusing with its calcifi ed wall by means of protuberances or
crests of the wall (sometimes present only at the edge of the
ovicell fl oor) transforming to skeletal crossbars. The fully
developed fl at ovicell fl oor is skirted by a low ooecial fold
of the non-calcifi ed frontal wall of the distal zooid. This fold
grows vertically and then centripetally, accompanied by progressive thickening of the calcifi ed entooecium.
2.3.2.5 The Case of Fenestrulina
In species of Fenestrulina (Microporellidae), the fl oor of the
brood cavity comprises entooecium fused with the proximal
area of the frontal shield of the distal autozooid by means of
several (16–18) radial crossbars; spaces between them
describe an arch of pores around the entooecial base
(Figs. 2.1 , 2.8D , 2.43E, F , 2.45 , and 2.65B ). Between the
ovicell fl oor and the proximal part of the frontal shield, a narrow coelomic space is retained that communicates with the
ooecial coelom via the pores between the crossbars. The
entooecium is surrounded by a raised lip, with a narrow rim
of gymnocyst (Fig. 2.43E–F ), that represents the calcifi ed
base of the ectooecium and the site where its non-calcifi ed
part is attached to the frontal shield. Because of this lip, the
ooecial coelom is isolated from the hypostegal coelom of the
distal zooid. The narrow ooecial cavity communicates with
the visceral coelom of the distal autozooid via a central slitlike pore; it is arched and located near the transverse wall
between the maternal and distal zooids (Figs. 2.1 , 2.8D ,
2.45 , and 2.65B ; see also Nielsen 1981 , fi g. 18B).
The ooecium is formed as an arched fold in the proximal
part of peripheral zooid buds in which formation of the
frontal shield is underway (Nielsen 1981 , fi gs. 17–19). The
earliest stage of calcifi cation of the provisional ovicell fl oor
is an unpaired tongue-like plate initiated from the transverse
zooidal wall. Further growth of the ooecial fold resembles
that in the lepralielliform variant although a double disc is
not formed (see Fig. 2.40 and description above).
The lower lateral areas of calcifi cation of the ooecial fold
grow towards each other, together with the proximal areas of
the developing frontal shield. Fusion of these areas beneath
the provisional ovicell fl oor (horizontal part of the entooecium) and formation of the calcifi ed base of ectooecium
result in separation of the coelomic cavity of the growing
ooecial fold from the hypostegal coelom of the distal zooid
and in the formation of the proximal part of its frontal shield
with central communication in the form of a slit-like pore
(Figs. 2.1 , 2.8D , and 2.45 ; see also Nielsen 1981 , Figs.
1.17B , 1.18 ). Further, the frontal shield fuses with the ovicell
fl oor by means of radial crossbars.
Fusion of the horizontal area of the entooecium with the
frontal shield and the lack of a double disc are microporelliform, whereas isolation of the ooecial and hypostegal
coeloms, the presence of the communication pore and early
ovicellogenesis are lepralielliform. It should also be noted
that, judging from the description of Nielsen ( 1981 ), F . miramara (as F . malusii ) has cleithral ovicells. In contrast, Calvet
( 1900 , fi g. 21) depicted an acleithral ovicell in F . malusii
(as Microporella ).
2.3 Structure and Development of Brood Chambers in Cheilostomata