139
Margarettidae (Fig. 2.37 ), Gigantoporidae, Cheiloporinidae,
Cyclicoporidae and Urceoliporidae (Fig. 1.23B ). Thus,
this ooecium seems to appear once a hypostegal coelom and
complex frontal wall have evolved.
The escharelliform ooecium is characterized by complete
or partial reduction of ectooecial calcifi cation and by fusion
of the entooecium with the cryptocyst or calcifi ed wall of the
frontal shield of the distal zooid. Uncalcifi ed ectooecium
continues to the membranous frontal wall of this zooid, while
the coelom of the ooecial fold is represented by a narrow
cavity communicating directly with the hypostegal coelom
of the distal zooid (Figs. 2.34 , 2.36 , and 2.37 ). A number of
species (for instance, Escharella immersa ) retain communication pores or a closed arched slit (Figs. 2.35C, H
and 2.36A ), highlighting ooecial communication with the
visceral coelom during the early stages of ooecial-fold formation (and evolution). Ooecia form at the colony periphery
(Fig. 2.35E–H ). The early stage of calcifi cation of the
provisional ovicell fl oor appears as a non-paired plate
(Fig. 2.35E, G ) (see also Levinsen 1909 , pl. 17, fi g. 3a). As it
forms, the ovicell fl oor fuses with the simultaneously
forming cryptocyst or the calcifi ed wall of the frontal shield
of the distal zooid (Fig. 2.35F, H ).
If the distal autozooid is reduced, the ooecial coelom
communicates with that of the ooecium-producing distal
kenozooid (via one or more pore that remain after closure
of the communication slit, presumably plugged by nonspecialized cells (in some species of Micropora ; see
Figs. 2.6a (C) and 2.33 D)) or the maternal autozooid (via one
or more pores with a pore-cell complex ( Mollia multijuncta )
(Fig. 1.28C, D )). In these two cases, ooecial structure fully
corresponds to the calloporiform type.
Crepis longipes (recently moved from the Chlidoniidae to
the Calloporidae) has partially calcifi ed ooecia formed by
the distal autozooid or distal kenozooid (see Harmelin and
d’Hondt 1992 ; Reverter-Gil et al. 2011 ). In the former case
the ooecial coelomic cavity communicates directly with the
hypostegal coelom of the distal zooid – a situation unknown
in calloporids. In the latter, the ooecial coelom communicates with that of the ooecium-producing distal kenozooid.
Both variants are known among Microporidae.
In Margaretta barbata , the maternal autozooid and the
ovicell open into the lumen of the elongated, distally bent
tube of the peristome (Figs. 2.7a (D) and 2.37 ). Such ovicells are
referred to as peristomial. The walls of the entooecium and the
peristome are continuous, being represented by a thick calcifi ed
layer perforated by pseudopores and covered from the outside
by the hypostegal coelom and membranous frontal wall.
Immersed escharelliform ovicells, correspond in all their
main features (except for the non-calcifi ed ectooecium
and ooecial communication with the hypostegal coelom)
to the above-described ovicells of Crassimarginatella sp.
(Calloporidae), are found in Onychocella (Onychocellidae)
and Cheiloporina (Cheiloporinidae). Endozooidal ovicells
are found in Cellarinella (Sclerodomidae) and Polirhabdotos
(Metrarabdotosidae) (see Levinsen 1909 , pl. 24, fi g. 10;
Harmer 1957 , fi g. 94).
The endotoichal ovicells of cellariids, which resemble
endozooidal ovicells because of complete immersion of
the brood cavity, should be attributed to the same group since
their ooecia are represented by external membranous and
internal calcifi ed walls and the ooecial coelom communicates
with the hypostegal coelom(s) of the ooecium- producing
autozooid(s). Although the ovicell opens into the distal part
of the frontal surface of the maternal autozooid (Fig. 2.38D,
F–H ), the brood chamber is immersed in the proximal part of
the distal zooid and, often, the neighbouring distolateral
zooids, and its walls, except for the proximal (transverse) wall,
comprise the skeletal walls of these zooids (Figs. 1.19B–D ,
1.20D , 2.7b (F), and 2.39 ) (see also Calvet 1900 , pl. 6, fi g.
11). The brood cavity is limited from above by the proximal
and lateral areas of the frontal wall of the distal zooid and/or
two distolateral zooids (Fig. 1.20D ) as well as by the upper
horizontal part of the transverse zooid wall (proximal part of
the ooecial roof). The entrance to the brood chamber is
closed by a modifi ed ooecial vesicle, which plays the role
of ovicell operculum and brood sac at the same time
(Figs. 1.19B–D , 2.7b (F), and 2.39 ). Its coelomic cavity
communicates with the hypostegal coelom of the maternal
autozooid laterally from the zooidal opening. The distal area
of the maternal zooid’s frontal membrane continues into the
wall of the ooecial vesicle. The cuticle of the vesicle wall just
below the distal edge of the ovicell opening thickens to form
a sclerite (Figs. 1.19B, D and 2.39 ). It is approached by a
group of thick muscle bundles, the proximal ends of which
are attached to the transverse wall between the brood chamber and the cavity of the maternal zooid. Inside the brood
cavity the thin wall of the ooecial vesicle serves as a sheath
surrounding the embryo in the ovicell (Figs. 1.19B–D , 1.20A,
B , 1.29B , and 2.39 ). The distal part of the ooecial vesicle is
attached to the calcifi ed fl oor or roof of the ovicell
(Figs. 2.7b (F) and 2.39 ).
2.3.2.3 The Lepralielliform Ooecium
As with the escharelliform type, the general form of construction of the lepralielliform variant corresponds to the calloporid
ooecium. The main differences from the escharelliform are
(1) partly or completely calcifi ed ectooecium, (2) communication of the ooecial coelom with that of the distal zooid via
a central communication pore (in most cases), (3) secondary
calcifi cation overgrowing the ooecium (several exceptions),
and (4) reduced ooecial base and early calcifi cation of the
ooecial fold as a “double disc” (some exceptions). The lepralielliform ooecium occurs in some hiantoporid and bugulid
anascans ( Bugula , Bicellariella ) (Figs. 1.18A, B , 2.3 , 2.5 , and
2.7a (A)) and a number of ascophorans, e.g. some species in the
2.3 Structure and Development of Brood Chambers in Cheilostomata
Margarettidae (Fig. 2.37 ), Gigantoporidae, Cheiloporinidae,
Cyclicoporidae and Urceoliporidae (Fig. 1.23B ). Thus,
this ooecium seems to appear once a hypostegal coelom and
complex frontal wall have evolved.
The escharelliform ooecium is characterized by complete
or partial reduction of ectooecial calcifi cation and by fusion
of the entooecium with the cryptocyst or calcifi ed wall of the
frontal shield of the distal zooid. Uncalcifi ed ectooecium
continues to the membranous frontal wall of this zooid, while
the coelom of the ooecial fold is represented by a narrow
cavity communicating directly with the hypostegal coelom
of the distal zooid (Figs. 2.34 , 2.36 , and 2.37 ). A number of
species (for instance, Escharella immersa ) retain communication pores or a closed arched slit (Figs. 2.35C, H
and 2.36A ), highlighting ooecial communication with the
visceral coelom during the early stages of ooecial-fold formation (and evolution). Ooecia form at the colony periphery
(Fig. 2.35E–H ). The early stage of calcifi cation of the
provisional ovicell fl oor appears as a non-paired plate
(Fig. 2.35E, G ) (see also Levinsen 1909 , pl. 17, fi g. 3a). As it
forms, the ovicell fl oor fuses with the simultaneously
forming cryptocyst or the calcifi ed wall of the frontal shield
of the distal zooid (Fig. 2.35F, H ).
If the distal autozooid is reduced, the ooecial coelom
communicates with that of the ooecium-producing distal
kenozooid (via one or more pore that remain after closure
of the communication slit, presumably plugged by nonspecialized cells (in some species of Micropora ; see
Figs. 2.6a (C) and 2.33 D)) or the maternal autozooid (via one
or more pores with a pore-cell complex ( Mollia multijuncta )
(Fig. 1.28C, D )). In these two cases, ooecial structure fully
corresponds to the calloporiform type.
Crepis longipes (recently moved from the Chlidoniidae to
the Calloporidae) has partially calcifi ed ooecia formed by
the distal autozooid or distal kenozooid (see Harmelin and
d’Hondt 1992 ; Reverter-Gil et al. 2011 ). In the former case
the ooecial coelomic cavity communicates directly with the
hypostegal coelom of the distal zooid – a situation unknown
in calloporids. In the latter, the ooecial coelom communicates with that of the ooecium-producing distal kenozooid.
Both variants are known among Microporidae.
In Margaretta barbata , the maternal autozooid and the
ovicell open into the lumen of the elongated, distally bent
tube of the peristome (Figs. 2.7a (D) and 2.37 ). Such ovicells are
referred to as peristomial. The walls of the entooecium and the
peristome are continuous, being represented by a thick calcifi ed
layer perforated by pseudopores and covered from the outside
by the hypostegal coelom and membranous frontal wall.
Immersed escharelliform ovicells, correspond in all their
main features (except for the non-calcifi ed ectooecium
and ooecial communication with the hypostegal coelom)
to the above-described ovicells of Crassimarginatella sp.
(Calloporidae), are found in Onychocella (Onychocellidae)
and Cheiloporina (Cheiloporinidae). Endozooidal ovicells
are found in Cellarinella (Sclerodomidae) and Polirhabdotos
(Metrarabdotosidae) (see Levinsen 1909 , pl. 24, fi g. 10;
Harmer 1957 , fi g. 94).
The endotoichal ovicells of cellariids, which resemble
endozooidal ovicells because of complete immersion of
the brood cavity, should be attributed to the same group since
their ooecia are represented by external membranous and
internal calcifi ed walls and the ooecial coelom communicates
with the hypostegal coelom(s) of the ooecium- producing
autozooid(s). Although the ovicell opens into the distal part
of the frontal surface of the maternal autozooid (Fig. 2.38D,
F–H ), the brood chamber is immersed in the proximal part of
the distal zooid and, often, the neighbouring distolateral
zooids, and its walls, except for the proximal (transverse) wall,
comprise the skeletal walls of these zooids (Figs. 1.19B–D ,
1.20D , 2.7b (F), and 2.39 ) (see also Calvet 1900 , pl. 6, fi g.
11). The brood cavity is limited from above by the proximal
and lateral areas of the frontal wall of the distal zooid and/or
two distolateral zooids (Fig. 1.20D ) as well as by the upper
horizontal part of the transverse zooid wall (proximal part of
the ooecial roof). The entrance to the brood chamber is
closed by a modifi ed ooecial vesicle, which plays the role
of ovicell operculum and brood sac at the same time
(Figs. 1.19B–D , 2.7b (F), and 2.39 ). Its coelomic cavity
communicates with the hypostegal coelom of the maternal
autozooid laterally from the zooidal opening. The distal area
of the maternal zooid’s frontal membrane continues into the
wall of the ooecial vesicle. The cuticle of the vesicle wall just
below the distal edge of the ovicell opening thickens to form
a sclerite (Figs. 1.19B, D and 2.39 ). It is approached by a
group of thick muscle bundles, the proximal ends of which
are attached to the transverse wall between the brood chamber and the cavity of the maternal zooid. Inside the brood
cavity the thin wall of the ooecial vesicle serves as a sheath
surrounding the embryo in the ovicell (Figs. 1.19B–D , 1.20A,
B , 1.29B , and 2.39 ). The distal part of the ooecial vesicle is
attached to the calcifi ed fl oor or roof of the ovicell
(Figs. 2.7b (F) and 2.39 ).
2.3.2.3 The Lepralielliform Ooecium
As with the escharelliform type, the general form of construction of the lepralielliform variant corresponds to the calloporid
ooecium. The main differences from the escharelliform are
(1) partly or completely calcifi ed ectooecium, (2) communication of the ooecial coelom with that of the distal zooid via
a central communication pore (in most cases), (3) secondary
calcifi cation overgrowing the ooecium (several exceptions),
and (4) reduced ooecial base and early calcifi cation of the
ooecial fold as a “double disc” (some exceptions). The lepralielliform ooecium occurs in some hiantoporid and bugulid
anascans ( Bugula , Bicellariella ) (Figs. 1.18A, B , 2.3 , 2.5 , and
2.7a (A)) and a number of ascophorans, e.g. some species in the
2.3 Structure and Development of Brood Chambers in Cheilostomata