127
cases the fl oor of the brood cavity is entirely or mainly
formed by the distal (ooecium-producing) zooid, which is
sometimes strongly fl attened (Figs. 1.36B, C , 2.6a (F), b (D, F),
and 2.42 ). The basal part of the ooecial fold can be positioned near the transverse wall between the maternal and
distal zooids or at a distance from it (compare Fig. 1 in
Introduction and Figs. 2.3 , 2.6a (A), and 2.7a (A)). Distal
budding in ooecium- producing zooid is, as a rule, retained.
If the distal kenozooid has no distally distinct frontal part,
the entire structure (ooecial fold plus distal kenozooid) may
be considered as a kenozooid that is formed by the maternal
autozooid, exemplifying so-called “terminal” ovicells (Figs.
1.27D , 1.30B , 1.36 , 2.6a (C, E, F), 2.23A , 2.33D , and 2.42B )
(Ostrovsky 1998 ). In fact, in this case, the maternal autozooid fi rst forms the distal bud (kenozooid), which in turn
forms the ooecial outfold (vertical walls and roof of the ooecium) (Figs. 1.36B, C , 2.6a (C, E), 2.17A, B , 2.23A , and
2.42B ). Thus, the upper wall of the distal kenozooid serves
as the fl oor of the brood cavity and the ooecium itself is an
outgrowth of this basally placed “ooecial kenozooid”
(Ostrovsky 2008b , see also illustrations in Levinsen 1909 ). In
other words, the entire skeletal structure consists of two
well- defi ned elements, only one of which is a kenozooid.
The “type 2” ooecium is itself a kenozooid, budded from
the maternal autozooid, and ovicells with such ooecia can be
also called terminal in some species (Figs. 1.25A , 1.28C, D ,
2.6a (D), b (A–C), and 2.29 ). The base (basal part adjacent to
maternal zooid) of such a “kenozooidal ooecium” is homologous with the strongly reduced distal kenozooid in ovicells
with “type 1” ooecia, whereas the rest of the ooecium is an
outfold. In contrast to “type 1”, the fl oor of the brood cavity in ovicells with “type 2” ooecia is formed entirely or partially by the distal wall of the maternal zooid. Kenozooidal
ooecia show various degrees of reduction (Figs. 1.25A ,
1.28C, D , 1.32A, B , 2.6a(D) , b (A–C, E), 2.7b (C), 2.25B , and
2.29 ), with the two types representing a clear evolutionary
trend towards reduction of the distal, ooecium-producing
zooid (Ostrovsky 1998 , 2008b , 2009 ; Ostrovsky et al. 2009a ,
see also illustrations in Levinsen 1909 ). Two examples with
intermediate morphology have been found (Figs. 1.25A ,
2.6a (D), and b (C)) that may be referred to as an “intermediate type”. Here, a kenozooidal ooecium is budded from the
maternal autozooid. The distal part of the ovicell fl oor is
formed by the ooecium, whereas the proximal part is formed
by the distal wall of the maternal autozooid (see also pl. 12,
fi g. 1h in Levinsen 1909 ).
It should be noted that the above categorization is a little
different from that introduced earlier (Ostrovsky 1998 ), in
which ooecia of all terminal ovicells (i.e. ovicells without a
distally distinct distal zooid) were considered to be formed
from the maternal zooid (discussed also in Ostrovsky
2008b ). For instance, according to Bishop and Househam
( 1987 ), all ooecia formed by the ooecium-producing distal
kenozooid with no distinct frontal part [not visible in frontal
view] (Figs. 2.6a (C, E), b (F), 2.23A , and 2.42 ) should be
considered as maternally derived and placed in “category
C” (see also Ostrovsky 1998 ). Instead, I propose that the
term “category C” should be used only for kenozooidal
ooecia (Figs. 1.25A , 1.28C, D , 1.32A, B , 2.6a (D), b (A–C),
and 2.29 ). Recently, Berning and Ostrovsky ( 2011 )
described ooecia that are budded from the distofrontal wall
of the maternal autozooid in Omanipora pilleri , stating that
similar “kenozooidal ooecia” (i.e. category C) are formed in
the genera Celleporina , Galeopsis and Turbicellepora s. str.
(Fig. 2.42 ). However, I have reconsidered this interpretation; the basal part of the brood chamber corresponds to a
strongly reduced distal ooecial kenozooid (Fig. 2.6b (D))
that forms both the ovicell fl oor and the ooecial outfold in
these cheilostomes. Thus, these ooecia should belong to category B.
Recognizing the locus of ooecium formation and interpreting its structure can be diffi cult without making sections
(compare, for instance, Fig. 2.6a (A) with Fig. 2.6b (B, F)):
compact zooidal budding, very narrow communications
between ooecial and zooidal coeloms, and structural variability often hamper this work. To avoid confusion, it is
better not to describe the type of ooecium formation if it is
uncertain. In the case of ovicells in which the underlying
distal zooid is not visible in frontal view (regardless of which
type of ooecium formation) (Figs. 1.25A , 1.27D , 1.28C, D ,
1.30B , 1.32A, B , 1.36 , 2.6a (C–F), b (A–C), 2.17A, B , 2.23A ,
2.29 , 2.33D , 2.42B , 2.60E , and 2.61E ), the descriptor “terminal” is proposed instead (see above), which may serve as
a compromise until their proper structure is determined.
Terminal ovicells are commonly (but not invariably) present
at the colony periphery, and are afterwards distinctly
separated from the zooids distal to them by a suture/slit
between the skeletal walls (Harmelin and Arístegui 1988 )
(Figs. 1.28D and 2.6b (B)).
2.2.2 Immersion of Brood Cavity
Another character used in ovicell classifi cation is the degree
to which the brood cavity is immersed in relation to the
colony surface.
The commonest type of ovicell in this regard is “hyperstomial”, i.e. positioned above the cavity of the underlying
(distal) zooid (“seated over the zooecia” in Levinsen 1902 ,
p. 13, and “situated outside the cavity of the zooecium” in
Levinsen 1909 , p. 60), although the word itself refl ects more
the position of the brood chamber relative to the opening of
the maternal zooid. Earlier, Busk ( 1884 ) had used “erect” for
such ooecia, and Jullien ( 1888 ) described variants of this
position as “superovicellate” and “subovicellate” (discussed
in Ryland 1968 ). However, most researchers have used and
2.2 Classifi cation and Terminology
cases the fl oor of the brood cavity is entirely or mainly
formed by the distal (ooecium-producing) zooid, which is
sometimes strongly fl attened (Figs. 1.36B, C , 2.6a (F), b (D, F),
and 2.42 ). The basal part of the ooecial fold can be positioned near the transverse wall between the maternal and
distal zooids or at a distance from it (compare Fig. 1 in
Introduction and Figs. 2.3 , 2.6a (A), and 2.7a (A)). Distal
budding in ooecium- producing zooid is, as a rule, retained.
If the distal kenozooid has no distally distinct frontal part,
the entire structure (ooecial fold plus distal kenozooid) may
be considered as a kenozooid that is formed by the maternal
autozooid, exemplifying so-called “terminal” ovicells (Figs.
1.27D , 1.30B , 1.36 , 2.6a (C, E, F), 2.23A , 2.33D , and 2.42B )
(Ostrovsky 1998 ). In fact, in this case, the maternal autozooid fi rst forms the distal bud (kenozooid), which in turn
forms the ooecial outfold (vertical walls and roof of the ooecium) (Figs. 1.36B, C , 2.6a (C, E), 2.17A, B , 2.23A , and
2.42B ). Thus, the upper wall of the distal kenozooid serves
as the fl oor of the brood cavity and the ooecium itself is an
outgrowth of this basally placed “ooecial kenozooid”
(Ostrovsky 2008b , see also illustrations in Levinsen 1909 ). In
other words, the entire skeletal structure consists of two
well- defi ned elements, only one of which is a kenozooid.
The “type 2” ooecium is itself a kenozooid, budded from
the maternal autozooid, and ovicells with such ooecia can be
also called terminal in some species (Figs. 1.25A , 1.28C, D ,
2.6a (D), b (A–C), and 2.29 ). The base (basal part adjacent to
maternal zooid) of such a “kenozooidal ooecium” is homologous with the strongly reduced distal kenozooid in ovicells
with “type 1” ooecia, whereas the rest of the ooecium is an
outfold. In contrast to “type 1”, the fl oor of the brood cavity in ovicells with “type 2” ooecia is formed entirely or partially by the distal wall of the maternal zooid. Kenozooidal
ooecia show various degrees of reduction (Figs. 1.25A ,
1.28C, D , 1.32A, B , 2.6a(D) , b (A–C, E), 2.7b (C), 2.25B , and
2.29 ), with the two types representing a clear evolutionary
trend towards reduction of the distal, ooecium-producing
zooid (Ostrovsky 1998 , 2008b , 2009 ; Ostrovsky et al. 2009a ,
see also illustrations in Levinsen 1909 ). Two examples with
intermediate morphology have been found (Figs. 1.25A ,
2.6a (D), and b (C)) that may be referred to as an “intermediate type”. Here, a kenozooidal ooecium is budded from the
maternal autozooid. The distal part of the ovicell fl oor is
formed by the ooecium, whereas the proximal part is formed
by the distal wall of the maternal autozooid (see also pl. 12,
fi g. 1h in Levinsen 1909 ).
It should be noted that the above categorization is a little
different from that introduced earlier (Ostrovsky 1998 ), in
which ooecia of all terminal ovicells (i.e. ovicells without a
distally distinct distal zooid) were considered to be formed
from the maternal zooid (discussed also in Ostrovsky
2008b ). For instance, according to Bishop and Househam
( 1987 ), all ooecia formed by the ooecium-producing distal
kenozooid with no distinct frontal part [not visible in frontal
view] (Figs. 2.6a (C, E), b (F), 2.23A , and 2.42 ) should be
considered as maternally derived and placed in “category
C” (see also Ostrovsky 1998 ). Instead, I propose that the
term “category C” should be used only for kenozooidal
ooecia (Figs. 1.25A , 1.28C, D , 1.32A, B , 2.6a (D), b (A–C),
and 2.29 ). Recently, Berning and Ostrovsky ( 2011 )
described ooecia that are budded from the distofrontal wall
of the maternal autozooid in Omanipora pilleri , stating that
similar “kenozooidal ooecia” (i.e. category C) are formed in
the genera Celleporina , Galeopsis and Turbicellepora s. str.
(Fig. 2.42 ). However, I have reconsidered this interpretation; the basal part of the brood chamber corresponds to a
strongly reduced distal ooecial kenozooid (Fig. 2.6b (D))
that forms both the ovicell fl oor and the ooecial outfold in
these cheilostomes. Thus, these ooecia should belong to category B.
Recognizing the locus of ooecium formation and interpreting its structure can be diffi cult without making sections
(compare, for instance, Fig. 2.6a (A) with Fig. 2.6b (B, F)):
compact zooidal budding, very narrow communications
between ooecial and zooidal coeloms, and structural variability often hamper this work. To avoid confusion, it is
better not to describe the type of ooecium formation if it is
uncertain. In the case of ovicells in which the underlying
distal zooid is not visible in frontal view (regardless of which
type of ooecium formation) (Figs. 1.25A , 1.27D , 1.28C, D ,
1.30B , 1.32A, B , 1.36 , 2.6a (C–F), b (A–C), 2.17A, B , 2.23A ,
2.29 , 2.33D , 2.42B , 2.60E , and 2.61E ), the descriptor “terminal” is proposed instead (see above), which may serve as
a compromise until their proper structure is determined.
Terminal ovicells are commonly (but not invariably) present
at the colony periphery, and are afterwards distinctly
separated from the zooids distal to them by a suture/slit
between the skeletal walls (Harmelin and Arístegui 1988 )
(Figs. 1.28D and 2.6b (B)).
2.2.2 Immersion of Brood Cavity
Another character used in ovicell classifi cation is the degree
to which the brood cavity is immersed in relation to the
colony surface.
The commonest type of ovicell in this regard is “hyperstomial”, i.e. positioned above the cavity of the underlying
(distal) zooid (“seated over the zooecia” in Levinsen 1902 ,
p. 13, and “situated outside the cavity of the zooecium” in
Levinsen 1909 , p. 60), although the word itself refl ects more
the position of the brood chamber relative to the opening of
the maternal zooid. Earlier, Busk ( 1884 ) had used “erect” for
such ooecia, and Jullien ( 1888 ) described variants of this
position as “superovicellate” and “subovicellate” (discussed
in Ryland 1968 ). However, most researchers have used and
2.2 Classifi cation and Terminology