146
is formed at the expense of an underlying basal kenozooid
that is budded from the maternal autozooid; in B . bilaminata
a vestigial kenozooidal ooecium is retained as a small, somewhat bent, calcifi ed hollow visor-like outgrowth at the distal
edge of the maternal autozooid (Fig. 1.22 ). Overall, the
structure of the brood chamber in this species is as in the
calloporid genus Cauloramphus (Figs. 2.6b (E), 2.7b (C), and
2.25B ) (Ostrovsky et al. 2007 , 2009a ).
A long neck also characterizes the brood sac of Arctonula
arctica (Romancheinidae), which may contain two embryos
at a time. In this instance, the chamber of the sac occupies
most of the coelom of the maternal autozooid. The
brood- chamber opening communicates with the environmental independently of the vestibulum, beneath the zooidal operculum.
Internal brood sacs develop in all Cupuladriidae. Sexual
zooidal polymorphism is lacking and the neck of the brood
sac communicates with the vestibulum. The distal wall of the
vestibulum bears a cuticular thickening (fl ap) above the
place where the neck opens into the vestibular cavity.
This fl ap may act like a cover, plugging the brood chamber
and providing additional isolation from the vestibulum
(Ostrovsky et al. 2009b ). In Steginoporella perplexa
(Steginoporellidae), the brood sac is situated under the
zooidal operculum as a large outpocket of the vestibulum.
In Watersipora subtorquata (Watersiporidae) (Figs. 2.7b (E)
and 2.47B ), the neck of the brood sac and the vestibulum
open to the exterior very near but independently of each
other, contradicting the photos of Mawatari ( 1952 ) in which
they fuse. This discrepancy could indicate that different
species were studied. My data on Cryptosula pallasiana
(Cryptosulidae) confi rm Calvet’s ( 1900 ) fi ndings that the
internal brood sac communicates with the vestibulum
(Figs. 2.7b (D) and 2.47A ).
In all the above species, there is no sexual zooidal polymorphism. In contrast, in Chlidonia pyriformis (Chlidoniidae),
Adeonella calveti (Adeonidae) and Reciprocus regalis
(Urceoliporidae), embryos develop in large female polymorphs. In the former species the brood sac and vestibulum
fuse immediately beneath the zooidal operculum. In the latter
two species the brood sac and vestibulum open independently and the inner vesicle plugging the entrance to the
brood cavity has a sclerite. A similar cuticular thickening
was found in Pleurotoichus clathratus (Euthyrisellidae), the
fertile zooids of which are characterized by an unusually
broad operculum base; its brood sac does not communicate
with the vestibulum.
Thus, although probably evolving independently in different cheilostome families (Ostrovsky et al. 2009b ; see also
Sect. 2.4.8 ), internal brood sacs have obvious morphological
similarities, differing mainly in mode of communication,
presence/absence of the inner vesicle and its sclerite, and
accompanying musculature.
2.3.4 Bivalved Ovicells
“Bivalved” brood chambers are characteristic of Scruparia
and Brettiopsis (Scrupariidae), Alysidium (Alysidiidae), and
Thalamoporella (Thalamoporellidae), which is why Hyman
( 1959 ) united them in a “two-valved” ovicell grouping.
Earlier, Harmer ( 1926 ) had compared thalamoporellid
ovicells with those of alysidiids, and Hastings ( 1941 ) noted
simultaneous brooding of several embryos in “two-valved
ovicells” in Scruparia and Thalamoporella .
Busk ( 1852 ) fi rst reported the brood chambers of
Alysidium parasiticum that were later studied in detail by
Levinsen ( 1902 , 1909 ). Each consists of two semispherical
hollow plates or “valves”, forming a protective chamber in
the distal part (top) of the maternal zooid. Each valve is
attached to the maternal zooid by a cuticular base that
permits them to bend outwards. Levinsen ( 1902 , p. 16)
called these brood chambers “bivalvular” or “double-valved
ooecia”, interpreting their valves as equivalent to oral spines
in non-fertile zooids. He subsequently showed that the
ooecial valves are true kenozooids whose cavity is separated
from the visceral coelom of the maternal zooid by a pore
plate (Levinsen 1909 , p. 66).
An unusually complex brood chamber (termed a synecium)
of six fl at plates (presumable kenozooids) was discovered by
O’Donoghue ( 1924 , p. 28) in the confamilial genus Catenicula
(see also O’Donoghue and Watteville 1944 , p. 423). The
plates “all curve over the opesium” [sic] of the fertile zooid,
forming “a globular basket-like arrangement in which the
early development of the young animal takes place.” Each plate
is attached to the maternal zooid or an adjacent plate by an
elastic cuticular joint. Hyman ( 1959 , p. 337) considered this
arrangement to be “related to the two- valved type”. Cook
( 1979 , p. 202) has used the modifi ed term “synoecium”.
In Scruparia (Scrupariidae), embryos are brooded in
large terminal ovicells (Fig. 2.48 ). For instance, Scruparia
ambigua has a high, galeate, terminally pointed ooecium
(Fig. 2.48B, D ) made of two halves. It has a medial longitudinal septum with a corresponding suture visible externally
and internally, ending on the outer basal surface as an arched
horizontal slit (Fig. 2.48C ). The septum results from the
medial fusion of two symmetrical, hollow, elongated lobes,
the coeloms of which are completely separated from each
other. They presumably communicate with the visceral coelom
of the maternal autozooid via communication pores with
pore-cell complexes in the distal wall of the latter, but, in the
absence of fixed material, this could not be confirmed
anatomically. If so, each ooecial lobe is a kenozooid budded
from the maternal autozooid. The ectooecium is mostly
membranous (except for the edges of each lobe), whereas the
entooecium is completely calcifi ed. Ovicells are semicleithral or acleithral (see Mawatari 1973a ) – the ovicell
opening is closed by the distal wall of the maternal autozooid
2 Cheilostome Brood Chambers: Structure, Formation, Evolution
is formed at the expense of an underlying basal kenozooid
that is budded from the maternal autozooid; in B . bilaminata
a vestigial kenozooidal ooecium is retained as a small, somewhat bent, calcifi ed hollow visor-like outgrowth at the distal
edge of the maternal autozooid (Fig. 1.22 ). Overall, the
structure of the brood chamber in this species is as in the
calloporid genus Cauloramphus (Figs. 2.6b (E), 2.7b (C), and
2.25B ) (Ostrovsky et al. 2007 , 2009a ).
A long neck also characterizes the brood sac of Arctonula
arctica (Romancheinidae), which may contain two embryos
at a time. In this instance, the chamber of the sac occupies
most of the coelom of the maternal autozooid. The
brood- chamber opening communicates with the environmental independently of the vestibulum, beneath the zooidal operculum.
Internal brood sacs develop in all Cupuladriidae. Sexual
zooidal polymorphism is lacking and the neck of the brood
sac communicates with the vestibulum. The distal wall of the
vestibulum bears a cuticular thickening (fl ap) above the
place where the neck opens into the vestibular cavity.
This fl ap may act like a cover, plugging the brood chamber
and providing additional isolation from the vestibulum
(Ostrovsky et al. 2009b ). In Steginoporella perplexa
(Steginoporellidae), the brood sac is situated under the
zooidal operculum as a large outpocket of the vestibulum.
In Watersipora subtorquata (Watersiporidae) (Figs. 2.7b (E)
and 2.47B ), the neck of the brood sac and the vestibulum
open to the exterior very near but independently of each
other, contradicting the photos of Mawatari ( 1952 ) in which
they fuse. This discrepancy could indicate that different
species were studied. My data on Cryptosula pallasiana
(Cryptosulidae) confi rm Calvet’s ( 1900 ) fi ndings that the
internal brood sac communicates with the vestibulum
(Figs. 2.7b (D) and 2.47A ).
In all the above species, there is no sexual zooidal polymorphism. In contrast, in Chlidonia pyriformis (Chlidoniidae),
Adeonella calveti (Adeonidae) and Reciprocus regalis
(Urceoliporidae), embryos develop in large female polymorphs. In the former species the brood sac and vestibulum
fuse immediately beneath the zooidal operculum. In the latter
two species the brood sac and vestibulum open independently and the inner vesicle plugging the entrance to the
brood cavity has a sclerite. A similar cuticular thickening
was found in Pleurotoichus clathratus (Euthyrisellidae), the
fertile zooids of which are characterized by an unusually
broad operculum base; its brood sac does not communicate
with the vestibulum.
Thus, although probably evolving independently in different cheilostome families (Ostrovsky et al. 2009b ; see also
Sect. 2.4.8 ), internal brood sacs have obvious morphological
similarities, differing mainly in mode of communication,
presence/absence of the inner vesicle and its sclerite, and
accompanying musculature.
2.3.4 Bivalved Ovicells
“Bivalved” brood chambers are characteristic of Scruparia
and Brettiopsis (Scrupariidae), Alysidium (Alysidiidae), and
Thalamoporella (Thalamoporellidae), which is why Hyman
( 1959 ) united them in a “two-valved” ovicell grouping.
Earlier, Harmer ( 1926 ) had compared thalamoporellid
ovicells with those of alysidiids, and Hastings ( 1941 ) noted
simultaneous brooding of several embryos in “two-valved
ovicells” in Scruparia and Thalamoporella .
Busk ( 1852 ) fi rst reported the brood chambers of
Alysidium parasiticum that were later studied in detail by
Levinsen ( 1902 , 1909 ). Each consists of two semispherical
hollow plates or “valves”, forming a protective chamber in
the distal part (top) of the maternal zooid. Each valve is
attached to the maternal zooid by a cuticular base that
permits them to bend outwards. Levinsen ( 1902 , p. 16)
called these brood chambers “bivalvular” or “double-valved
ooecia”, interpreting their valves as equivalent to oral spines
in non-fertile zooids. He subsequently showed that the
ooecial valves are true kenozooids whose cavity is separated
from the visceral coelom of the maternal zooid by a pore
plate (Levinsen 1909 , p. 66).
An unusually complex brood chamber (termed a synecium)
of six fl at plates (presumable kenozooids) was discovered by
O’Donoghue ( 1924 , p. 28) in the confamilial genus Catenicula
(see also O’Donoghue and Watteville 1944 , p. 423). The
plates “all curve over the opesium” [sic] of the fertile zooid,
forming “a globular basket-like arrangement in which the
early development of the young animal takes place.” Each plate
is attached to the maternal zooid or an adjacent plate by an
elastic cuticular joint. Hyman ( 1959 , p. 337) considered this
arrangement to be “related to the two- valved type”. Cook
( 1979 , p. 202) has used the modifi ed term “synoecium”.
In Scruparia (Scrupariidae), embryos are brooded in
large terminal ovicells (Fig. 2.48 ). For instance, Scruparia
ambigua has a high, galeate, terminally pointed ooecium
(Fig. 2.48B, D ) made of two halves. It has a medial longitudinal septum with a corresponding suture visible externally
and internally, ending on the outer basal surface as an arched
horizontal slit (Fig. 2.48C ). The septum results from the
medial fusion of two symmetrical, hollow, elongated lobes,
the coeloms of which are completely separated from each
other. They presumably communicate with the visceral coelom
of the maternal autozooid via communication pores with
pore-cell complexes in the distal wall of the latter, but, in the
absence of fixed material, this could not be confirmed
anatomically. If so, each ooecial lobe is a kenozooid budded
from the maternal autozooid. The ectooecium is mostly
membranous (except for the edges of each lobe), whereas the
entooecium is completely calcifi ed. Ovicells are semicleithral or acleithral (see Mawatari 1973a ) – the ovicell
opening is closed by the distal wall of the maternal autozooid
2 Cheilostome Brood Chambers: Structure, Formation, Evolution