50
multiply, surrounding mature oocytes in the centre. She
reported oocyte development as being accompanied by slow
fusion with the “nourishing cell” (“Nährzelle”). These cells
allegedly “belong to the ovarian wall” (Bonnevie 1907 , р.
585), and the nucleus of the nourishing cell remains noticeable in the cytoplasm of the oocyte for some time. This
description is reminiscent of the formation of oocyte doublets by cell fusion in the brooding cheilostome
Thalamoporella evelinae (Marcus 1941a ), not recorded in
any other bryozoan (see below). Further studies are necessary to determine if these data are correct.
According to Bonnevie ( 1907 ), the fi rst maturation division in Electra pilosa , accompanied by degeneration of the
nuclear envelope, begins while the oocyte is still in the ovary
and is interrupted after ovulation. Similar data on oocyte
meiosis were obtained by Temkin ( 1994 ) in Membranipora
membranacea . Bonnevie noted that ovulated eggs increase
in size while in the zooid coelom. Temkin (personal communication, 2002) thought that this increase might result
from water uptake. According to his data (Temkin 1996 ), the
size of late ovarian oocytes in Electra pilosa is 95–145 μm,
while the diameter of ovulated oocytes is 105–178 μm.
Enlargement of oocytes after ovulation in Electra posidoniae
can be seen in the drawings of Silén ( 1966 , fi gs. 3 and 4),
where oocytes about to be released are much larger than
those recently ovulated.
The maximum total number of female cells in a mature
ovary of Electra pilosa in my study was 25, with 10 more
ovulated oocytes being found in the zooid cavity. Their size
in sections was 65–80 × 40–50 μm, though, as noted above,
the irregular shape of oocytes often confounds measurement.
According to other authors, the number of ovarian oocytes in
this species may vary from fi ve to eight (Prouho 1892 ; Calvet
1900 ) to 20 (Bonnevie 1907 , pl. 35, fi g. 55) and even 31
(Temkin 1996 ). The maximum number of ovulated oocytes
found in a single zooid by Marcus ( 1926a ) was 17, with 10–20
additional oocytes remaining in the ovary after ovulation.
Ovulated oocytes were fl attened and irregular (ellipsoidal,
polygonal, crescentic, or sausage-shaped), attaining 80 μm
in size. Ten ovulated oocytes of irregular shape were
depicted by Prouho ( 1892 , pl. 25, fi g. 26). The zooid cavity
of E . pilosa (Temkin 1996 ) contained from 4 to 15 ovulated
oocytes, varying in size from 105 to 178 μm.
As for other Malacostegina, in Membranipora membranacea the number of ovarian oocytes may reach 40 (Smitt
1865 , pl. 7, fi g. 3) and coelomic oocytes 30 (Temkin 1996 ;
Temkin and Bortolami 2004 ), 39 (Silén 1945 , fi g. 9) or more
than 50 (as a rule, 10–20) (Eggleston 1963 , 1972 ). The diameter
of fl attened oocytes in different populations of this species
ranges from 70 μm (Silén 1945 ) to 80–120 × 80 μm (about 30 μm
thick) (Eggleston 1963 ) and 100 μm (Temkin, personal communication, 2002). Oocytes of M . isabelleana also attain a
diamer of 100 μm (Cancino et al. 1991 ). In M . serrilamella
the number of ovulated oocytes formed by a single fertile
zooid may be, according to different sources, from 20–25 to
40 or more, with a diameter of 85.8–101 μm (Hageman
1983 ; Zimmer, personal communication in Reed 1991 ) and
100 μm (Mawatari 1975 ; Mawatari and Mawatari 1975 ). The
number of ovulated oocytes per zooid ranges from 8–9 to 20
in Electra posidoniae , six (Silén 1966 ) to 16 (Borg 1947 ) in
Einhornia crustulenta , and 5–9 in E . monostachys (Cook
1964a ). Oocyte diameter in E . crustulenta attains 110 μm
(Cook 1962 ) and 100 × 70 μm in E . monostachys (Cook
1964a ). In species of Conopeum , the number and size of ovulated oocytes produced by a fertile zooid are respectively 5–6
and 65 × 45 μm (diameter of expelled egg) in C . tenuissimum
(Dudley 1973 ) and 5–9 and 110 × 80 μm in C . reticulum
(Cook 1964a ); Cook ( 1962 ) recorded oocyte size in C . seurati as 85 μm but did not mention oocyte number. It should be
noted that most of the authors cited above gave data on ovulated oocytes only. Actually, comparing the size (diameter
and volume) of mature oocytes in malacostegans is hampered by the fact that ovulated eggs are fl attened (in electrids,
they are also irregular). Moreover, the size and shape of
zygotes change considerably after liberation. For instance,
the mean diameter of fl at, ovulated, coelomic oocytes in M .
serrilamella is 100 μm, whereas the released, rounded zygote
never exceeds 50 μm diameter (Mawatari and Mawatari
1975 ) (see also Sect. 3.1.2 ).
According to the unpublished data of Temkin (personal
communication, 2002), the formation of oocytes in
M . membranacea under laboratory conditions takes 5–6 days
(from the time the ovary is fi rst visible by light microscopy
until spawning). This roughly corresponds to a period of
7–9 days for oogenesis in Electra posidoniae in laboratory
conditions (Silén 1966 ).
In all instances but one, malacostegan eggs are described
as numerous (5–50), small (90 μm on average) and yolkpoor (microlecithal/oligolecithal). A striking exception is
Arbocuspis bellula , which forms a single large egg (Marcus
1938a ). Since Marcus did not study the internal structure of
the fertile zooids or larval development, the continued
inclusion of this species in the Malacostegina is questionable. For instance, prior to discovering internal incubation in
“ Bifl ustra” perfragilis , which produces large macrolecithal
oocytes (Fig. 1.11A ) and broods embryos in internal sacs
(Fig. 2.46B ) (Ostrovsky et al. 2006 ), it was always attributed
to Malacostegina. It is evidently a neocheilostome and
requires a new genus.
The presence of groups of similar-sized oocytes, about to
ovulate or already ovulated, indicates that maturation and
ovulation are synchronous (Hageman 1983 ; Temkin 1996 ).
In some malacostegans spawning is also synchronized (see
above), lasting from 1 to 4 h ( E . posidoniae , M . membranacea ) to more than 4 days ( Einhornia crustulenta ) (Silén
1966 ; Temkin 1994 ).
1 Reproductive Patterns of Gymnolaemate Bryozoa: General Overview and Comparative Analysis
multiply, surrounding mature oocytes in the centre. She
reported oocyte development as being accompanied by slow
fusion with the “nourishing cell” (“Nährzelle”). These cells
allegedly “belong to the ovarian wall” (Bonnevie 1907 , р.
585), and the nucleus of the nourishing cell remains noticeable in the cytoplasm of the oocyte for some time. This
description is reminiscent of the formation of oocyte doublets by cell fusion in the brooding cheilostome
Thalamoporella evelinae (Marcus 1941a ), not recorded in
any other bryozoan (see below). Further studies are necessary to determine if these data are correct.
According to Bonnevie ( 1907 ), the fi rst maturation division in Electra pilosa , accompanied by degeneration of the
nuclear envelope, begins while the oocyte is still in the ovary
and is interrupted after ovulation. Similar data on oocyte
meiosis were obtained by Temkin ( 1994 ) in Membranipora
membranacea . Bonnevie noted that ovulated eggs increase
in size while in the zooid coelom. Temkin (personal communication, 2002) thought that this increase might result
from water uptake. According to his data (Temkin 1996 ), the
size of late ovarian oocytes in Electra pilosa is 95–145 μm,
while the diameter of ovulated oocytes is 105–178 μm.
Enlargement of oocytes after ovulation in Electra posidoniae
can be seen in the drawings of Silén ( 1966 , fi gs. 3 and 4),
where oocytes about to be released are much larger than
those recently ovulated.
The maximum total number of female cells in a mature
ovary of Electra pilosa in my study was 25, with 10 more
ovulated oocytes being found in the zooid cavity. Their size
in sections was 65–80 × 40–50 μm, though, as noted above,
the irregular shape of oocytes often confounds measurement.
According to other authors, the number of ovarian oocytes in
this species may vary from fi ve to eight (Prouho 1892 ; Calvet
1900 ) to 20 (Bonnevie 1907 , pl. 35, fi g. 55) and even 31
(Temkin 1996 ). The maximum number of ovulated oocytes
found in a single zooid by Marcus ( 1926a ) was 17, with 10–20
additional oocytes remaining in the ovary after ovulation.
Ovulated oocytes were fl attened and irregular (ellipsoidal,
polygonal, crescentic, or sausage-shaped), attaining 80 μm
in size. Ten ovulated oocytes of irregular shape were
depicted by Prouho ( 1892 , pl. 25, fi g. 26). The zooid cavity
of E . pilosa (Temkin 1996 ) contained from 4 to 15 ovulated
oocytes, varying in size from 105 to 178 μm.
As for other Malacostegina, in Membranipora membranacea the number of ovarian oocytes may reach 40 (Smitt
1865 , pl. 7, fi g. 3) and coelomic oocytes 30 (Temkin 1996 ;
Temkin and Bortolami 2004 ), 39 (Silén 1945 , fi g. 9) or more
than 50 (as a rule, 10–20) (Eggleston 1963 , 1972 ). The diameter
of fl attened oocytes in different populations of this species
ranges from 70 μm (Silén 1945 ) to 80–120 × 80 μm (about 30 μm
thick) (Eggleston 1963 ) and 100 μm (Temkin, personal communication, 2002). Oocytes of M . isabelleana also attain a
diamer of 100 μm (Cancino et al. 1991 ). In M . serrilamella
the number of ovulated oocytes formed by a single fertile
zooid may be, according to different sources, from 20–25 to
40 or more, with a diameter of 85.8–101 μm (Hageman
1983 ; Zimmer, personal communication in Reed 1991 ) and
100 μm (Mawatari 1975 ; Mawatari and Mawatari 1975 ). The
number of ovulated oocytes per zooid ranges from 8–9 to 20
in Electra posidoniae , six (Silén 1966 ) to 16 (Borg 1947 ) in
Einhornia crustulenta , and 5–9 in E . monostachys (Cook
1964a ). Oocyte diameter in E . crustulenta attains 110 μm
(Cook 1962 ) and 100 × 70 μm in E . monostachys (Cook
1964a ). In species of Conopeum , the number and size of ovulated oocytes produced by a fertile zooid are respectively 5–6
and 65 × 45 μm (diameter of expelled egg) in C . tenuissimum
(Dudley 1973 ) and 5–9 and 110 × 80 μm in C . reticulum
(Cook 1964a ); Cook ( 1962 ) recorded oocyte size in C . seurati as 85 μm but did not mention oocyte number. It should be
noted that most of the authors cited above gave data on ovulated oocytes only. Actually, comparing the size (diameter
and volume) of mature oocytes in malacostegans is hampered by the fact that ovulated eggs are fl attened (in electrids,
they are also irregular). Moreover, the size and shape of
zygotes change considerably after liberation. For instance,
the mean diameter of fl at, ovulated, coelomic oocytes in M .
serrilamella is 100 μm, whereas the released, rounded zygote
never exceeds 50 μm diameter (Mawatari and Mawatari
1975 ) (see also Sect. 3.1.2 ).
According to the unpublished data of Temkin (personal
communication, 2002), the formation of oocytes in
M . membranacea under laboratory conditions takes 5–6 days
(from the time the ovary is fi rst visible by light microscopy
until spawning). This roughly corresponds to a period of
7–9 days for oogenesis in Electra posidoniae in laboratory
conditions (Silén 1966 ).
In all instances but one, malacostegan eggs are described
as numerous (5–50), small (90 μm on average) and yolkpoor (microlecithal/oligolecithal). A striking exception is
Arbocuspis bellula , which forms a single large egg (Marcus
1938a ). Since Marcus did not study the internal structure of
the fertile zooids or larval development, the continued
inclusion of this species in the Malacostegina is questionable. For instance, prior to discovering internal incubation in
“ Bifl ustra” perfragilis , which produces large macrolecithal
oocytes (Fig. 1.11A ) and broods embryos in internal sacs
(Fig. 2.46B ) (Ostrovsky et al. 2006 ), it was always attributed
to Malacostegina. It is evidently a neocheilostome and
requires a new genus.
The presence of groups of similar-sized oocytes, about to
ovulate or already ovulated, indicates that maturation and
ovulation are synchronous (Hageman 1983 ; Temkin 1996 ).
In some malacostegans spawning is also synchronized (see
above), lasting from 1 to 4 h ( E . posidoniae , M . membranacea ) to more than 4 days ( Einhornia crustulenta ) (Silén
1966 ; Temkin 1994 ).
1 Reproductive Patterns of Gymnolaemate Bryozoa: General Overview and Comparative Analysis