140
umbonulomorph families Arachnopusiidae and Lepraliellidae
and presumably in all Bryocryptellidae and Umbonulidae
(Figs. 2.7a (G), 2.40 , and 2.41 ) and in the lepraliomorph
families Smittinidae, Bitectiporidae, Stomachetosellidae,
Lanceoporidae, Cleidochasmatidae, Phidoloporidae, Hippoporidridae, Celleporidae, Lekythoporidae, Petraliidae, and
Petraliellidae (Figs. 2.8E, F , 2.40 , 2.41 , and 2.65A ).
In Bugula and Bicellariella , the ooecium develops as a
small terminal evagination of the distal zooid bud, having a
narrow base (Nielsen 1985 ; Moosburgger et al. 2012 ). As the
initially funnel-shaped evagination enlarges, it broadens distally. Calcifi cation lags slightly behind ooecium formation.
Ooecial coelomic cavity communicates with the visceral
coelom of the distal zooid via a communication pore that is
partly or completely plugged by non-specialized epithelial
cells (Woollacott and Zimmer 1972a ; Moosburgger et al.
2012 ). As in the ascophorans described below, the following
stage of ooecial formation in bugulids is a slightly concave
“double disc”.
In most ascophorans with a lepralielliform ooecium, the
ectooecium is calcifi ed with small to medium-sized pseudopores, oval, rounded or irregular and evenly or unevenly
scattered on the surface. In some species the ectooecium has
membranous windows; in rare cases only the ectooecium
base is calcifi ed. In many species, as the colony ages, ooecia
are immersed completely or almost completely in secondary
calcifi cation (Figs. 2.7a (G), 2.8F , 2.40B , and 2.41A ) of the
frontal shield of the distal zooid and often 2–5 distolateral
autozooids. The boundaries of calcifi cation formed by the
adjacent zooids appear as sutures or crests (see Levinsen
1909 , pl. 18, fi g. 13a, pl. 24, fi g. 5a). The presence of such
sutures led some researchers to interpret the ooecia of
such ovicells as cormidial, i.e. formed by several zooids.
In other species secondary calcifi cation is weakly developed
(Fig. 2.41B, C ). The ooecium may also become immersed in
the colony by frontal budding of hypostegal coeloms, forming
additional zooid layers.
The ooecial cavity communicates with the visceral coelom
of the distal autozooid via a narrow communication canal
with a central pore (Figs. 2.7a (G), 2.8E, F , 2.40E , 2.41 , and
2.65A ). The pore is located close to the transverse wall
between maternal and distal zooids or at some distance from
it. The lumen of the communication canal is plugged by
non- specialized epithelial cells (Fig. 2.41 ). If the distal
autozooid is reduced, the ooecial coelom communicates via
a narrow slit with the coelom of the fl attened, ooeciumproducing distal kenozooid that in turn is connected with a
maternal autozooid via a communication pore(s) plugged by
a pore-cell complex (Figs. 2.6b (D, F) and 2.42 ). In this case,
ooecial structure can be described as calloporiform, whereas
early stages of ovicellogenesis correspond to the lepralielliform “double disc”.
Ooecia originate at the colony periphery (Fig. 2.40A, C ).
In general, ovicellogenesis starts with the formation of a fl at
hollow outgrowth (ooecial fold), which has the shape of a
semicircle with a narrow base surrounding the communication
pore (Fig. 2.40C, E, F ) (Banta 1977 ). Early stages of ooecial
fl oor calcifi cation are represented by a paired ( Porella smitti ,
Smittina mucronata ) (Fig. 2.40C, E ) or non-paired (most
species studied) plate. This plate represents the initial calcifi cation of the ooecial fold, which begins development at the
proximal part of the frontal shield of the distal zooid before
its calcifi cation is completed (Fig. 2.40C–E ). The lower lateral areas of ooecial-fold calcifi cation grow toward each
other together with the lateroproximal parts of the developing frontal shield (Fig. 2.40D ). The fusion of these areas and
the formation of the calcifi ed base of the ectooecium result in
separation of the coelomic cavity of the growing ooecial fold
from the hypostegal coelom of the distal zooid and formation
of the central communication pore (Fig. 2.40E ). Continued
growth of the ooecial fold occurs at its uncalcifi ed edge
(Fig. 2.40 inset) (see also Levinsen 1909 , pl. 19, fi g. 4a).
The lower wall of the ooecial fold (provisional ectooecium) overgrows the proximal part of the distal autozooid,
tightly adjoining its outer (frontal) non-calcifi ed wall
(Fig. 2.40F ), as a consequence of which both elements (autozooidal frontal membrane and ectooecial cuticle) become
immured between the subsequent ectooecial calcifi cation
and that of the frontal wall (i.e. frontal shield). The hypostegal coelom in the zone of overgrowth is compressed and
obliterated (Fig. 2.41A, C ) (Banta 1977 ). At this stage the
ooecial fold becomes a double disc consisting of the upper
non-paired plate (provisional entooecium, ovicell fl oor) and
the lower plate (ectooecium) (Fig. 2.40F ). After the horizontal
part of the ooecium has been formed, its vertical growth
starts, accompanied by a more-or-less synchronous overgrowing of the ooecium by a matrix of secondary calcifi cation at the expense of the thickening frontal shield of the
distal zooid. When forming the roof, the edges of the ooecium grow from the periphery to the centre.
A careful description and schematic of ovicellogenesis in
Reteporellina evelinae were published by Banta ( 1977 ) (for
illustrations of ovicellogenesis see also Hass ( 1948 ), Soule
( 1973 ), Cook ( 1977a ), Cook and Hayward ( 1983 ) and
Gordon and Grischenko ( 1994 )). Cook ( 1977a ) and Cook
and Chimonides ( 1981a ) carefully described and illustrated
ooecium formation in a number of species of Arachnopusiidae
and Petraliellidae. However, since they did not make sections,
both cuticular and calcifi ed walls (some excessive) in their
SEM-based descriptions and schemata are shown in a confusing manner.
In Rhamphostomella ovata , Palmiskenea sp. and some
other species, development of the ooecial fold differs from
that described above – formation of the double disk stage is
2 Cheilostome Brood Chambers: Structure, Formation, Evolution
umbonulomorph families Arachnopusiidae and Lepraliellidae
and presumably in all Bryocryptellidae and Umbonulidae
(Figs. 2.7a (G), 2.40 , and 2.41 ) and in the lepraliomorph
families Smittinidae, Bitectiporidae, Stomachetosellidae,
Lanceoporidae, Cleidochasmatidae, Phidoloporidae, Hippoporidridae, Celleporidae, Lekythoporidae, Petraliidae, and
Petraliellidae (Figs. 2.8E, F , 2.40 , 2.41 , and 2.65A ).
In Bugula and Bicellariella , the ooecium develops as a
small terminal evagination of the distal zooid bud, having a
narrow base (Nielsen 1985 ; Moosburgger et al. 2012 ). As the
initially funnel-shaped evagination enlarges, it broadens distally. Calcifi cation lags slightly behind ooecium formation.
Ooecial coelomic cavity communicates with the visceral
coelom of the distal zooid via a communication pore that is
partly or completely plugged by non-specialized epithelial
cells (Woollacott and Zimmer 1972a ; Moosburgger et al.
2012 ). As in the ascophorans described below, the following
stage of ooecial formation in bugulids is a slightly concave
“double disc”.
In most ascophorans with a lepralielliform ooecium, the
ectooecium is calcifi ed with small to medium-sized pseudopores, oval, rounded or irregular and evenly or unevenly
scattered on the surface. In some species the ectooecium has
membranous windows; in rare cases only the ectooecium
base is calcifi ed. In many species, as the colony ages, ooecia
are immersed completely or almost completely in secondary
calcifi cation (Figs. 2.7a (G), 2.8F , 2.40B , and 2.41A ) of the
frontal shield of the distal zooid and often 2–5 distolateral
autozooids. The boundaries of calcifi cation formed by the
adjacent zooids appear as sutures or crests (see Levinsen
1909 , pl. 18, fi g. 13a, pl. 24, fi g. 5a). The presence of such
sutures led some researchers to interpret the ooecia of
such ovicells as cormidial, i.e. formed by several zooids.
In other species secondary calcifi cation is weakly developed
(Fig. 2.41B, C ). The ooecium may also become immersed in
the colony by frontal budding of hypostegal coeloms, forming
additional zooid layers.
The ooecial cavity communicates with the visceral coelom
of the distal autozooid via a narrow communication canal
with a central pore (Figs. 2.7a (G), 2.8E, F , 2.40E , 2.41 , and
2.65A ). The pore is located close to the transverse wall
between maternal and distal zooids or at some distance from
it. The lumen of the communication canal is plugged by
non- specialized epithelial cells (Fig. 2.41 ). If the distal
autozooid is reduced, the ooecial coelom communicates via
a narrow slit with the coelom of the fl attened, ooeciumproducing distal kenozooid that in turn is connected with a
maternal autozooid via a communication pore(s) plugged by
a pore-cell complex (Figs. 2.6b (D, F) and 2.42 ). In this case,
ooecial structure can be described as calloporiform, whereas
early stages of ovicellogenesis correspond to the lepralielliform “double disc”.
Ooecia originate at the colony periphery (Fig. 2.40A, C ).
In general, ovicellogenesis starts with the formation of a fl at
hollow outgrowth (ooecial fold), which has the shape of a
semicircle with a narrow base surrounding the communication
pore (Fig. 2.40C, E, F ) (Banta 1977 ). Early stages of ooecial
fl oor calcifi cation are represented by a paired ( Porella smitti ,
Smittina mucronata ) (Fig. 2.40C, E ) or non-paired (most
species studied) plate. This plate represents the initial calcifi cation of the ooecial fold, which begins development at the
proximal part of the frontal shield of the distal zooid before
its calcifi cation is completed (Fig. 2.40C–E ). The lower lateral areas of ooecial-fold calcifi cation grow toward each
other together with the lateroproximal parts of the developing frontal shield (Fig. 2.40D ). The fusion of these areas and
the formation of the calcifi ed base of the ectooecium result in
separation of the coelomic cavity of the growing ooecial fold
from the hypostegal coelom of the distal zooid and formation
of the central communication pore (Fig. 2.40E ). Continued
growth of the ooecial fold occurs at its uncalcifi ed edge
(Fig. 2.40 inset) (see also Levinsen 1909 , pl. 19, fi g. 4a).
The lower wall of the ooecial fold (provisional ectooecium) overgrows the proximal part of the distal autozooid,
tightly adjoining its outer (frontal) non-calcifi ed wall
(Fig. 2.40F ), as a consequence of which both elements (autozooidal frontal membrane and ectooecial cuticle) become
immured between the subsequent ectooecial calcifi cation
and that of the frontal wall (i.e. frontal shield). The hypostegal coelom in the zone of overgrowth is compressed and
obliterated (Fig. 2.41A, C ) (Banta 1977 ). At this stage the
ooecial fold becomes a double disc consisting of the upper
non-paired plate (provisional entooecium, ovicell fl oor) and
the lower plate (ectooecium) (Fig. 2.40F ). After the horizontal
part of the ooecium has been formed, its vertical growth
starts, accompanied by a more-or-less synchronous overgrowing of the ooecium by a matrix of secondary calcifi cation at the expense of the thickening frontal shield of the
distal zooid. When forming the roof, the edges of the ooecium grow from the periphery to the centre.
A careful description and schematic of ovicellogenesis in
Reteporellina evelinae were published by Banta ( 1977 ) (for
illustrations of ovicellogenesis see also Hass ( 1948 ), Soule
( 1973 ), Cook ( 1977a ), Cook and Hayward ( 1983 ) and
Gordon and Grischenko ( 1994 )). Cook ( 1977a ) and Cook
and Chimonides ( 1981a ) carefully described and illustrated
ooecium formation in a number of species of Arachnopusiidae
and Petraliellidae. However, since they did not make sections,
both cuticular and calcifi ed walls (some excessive) in their
SEM-based descriptions and schemata are shown in a confusing manner.
In Rhamphostomella ovata , Palmiskenea sp. and some
other species, development of the ooecial fold differs from
that described above – formation of the double disk stage is
2 Cheilostome Brood Chambers: Structure, Formation, Evolution