307
seasons in particular and life cycles in general. Gordon
recognized three “breeding patterns” among 23 species of
New Zealand intertidal bryozoans, depending on the season
and duration of the reproductive activities. He also made an
attempt to classify their “brooding habits”. Interestingly, in
dissected ovicells of Macropora levinseni (as Macropora
grandis ), Gordon found 2–4 simultaneously brooding
embryos. Eggleston studied life cycles and reproductive patterns (terms and duration of reproductive season and colony
longevity), recording gonadal activity, brooding, spawning
and larval settlement in more than 50 species from the Isle of
Man. He divided them into four groups (those living less
than a year, annuals, biennials and perennials), depending on
colony longevity and the number of breeding/non-breeding
generations presented through the seasons. Interestingly,
Gautier ( 1962 ), who studied Mediterranean bryozoans,
found that seasonality is refl ected in reproduction to depths
of 20 m, whereas, at greater depths, the same species were
breeding for the most of the year. Eggleston ( 1972 ) showed
that the number of embryo-bearing zooids in the colony, the
size at which the colony starts reproduction, embryo size and
the rate of embryo development are related to the length of
the breeding season and colony longevity. In general, shorter
longevity means that a higher percentage of zooids brood,
their larvae are smaller and their development is faster. The
size at which the colony begins to reproduce is related to the
length of the breeding season and the longevity of the colony.
Most nearshore species have a short breeding period that is
probably connected with the variability of the shore environment. Eggleston also suggested that internally brooded
embryos are better protected against environmental variations, so internal brooders frequently occur in the upper
intertidal, where they are often exposed to drying. In
Bicellariella ciliata , Eggleston described sexual colony
zonation (sometimes repeated), and discovered external
brooding in the “membrane sacs” of Eucratea loricata along
with internal brooding of several embryos simultaneously in
Oshurkovia littoralis (as Umbonula ). Internal brooding in
this species was fi rst recorded by Hastings ( 1944 ), subsequently using the term “internal ovisac” (Hastings 1964 ).
Dudley ( 1973 ) observed reproduction in the cheilostome
Conopeum tenuissimum , recording the timing of gonad
appearance and the subsequent gamete release. Zooids in
this case are protandrous hermaphrodites, with the intertentacular organ developing after the fi rst polypide cycle.
Mawatari ( 1975 ) and Mawatari and Mawatari ( 1975 ) studied
a similar life cycle in Membranipora serrilamella . Zooids
are protandrous hermaphrodites. Testes develop just beneath
the lateral and proximal region of the membranous frontal
wall, whereas the ovary develops in the distal half of the
zooid [the wall is not specifi ed], and they recorded more than
40 ovulated eggs per zooid. Two or more eggs are usually
found in the intertentacular organ during their release.
Accidentally swallowed eggs are defaecated soon afterwards.
A fertilization envelope is formed after the liberation of the
zygote, which transforms from a fl attened circular disk to a
sphere with a diameter about half the size of the disk.
Interestingly, despite their numerous observations, they
failed to observe polar bodies, suggesting that these break
away and degrade at an early stage in this species.
Ryland ( 1970 , 1974 , 1976 , 1982 ) reviewed sexual reproduction in Bryozoa, including all major discoveries made
subsequent to Hyman ( 1959 ) and identifying the most important unsolved problems. Ryland ( 1976 ) characterized in
detail three reproductive patterns outlined by Harmer ( 1926 )
and Woollacott and Zimmer ( 1975 ), and suggested that byproducts from the degenerated polypide could be used for
extraembryonic nutrition. Among the most interesting of
Ryland’s conclusions based on Marcus’s ( 1938a ) fi ndings is
that there are different methods of brooding, with or without
placental nutrition, among related groups, sometimes within
the same genus. He also usefully summarised available data
on the increase in larval volume during placental brooding.
Describing the pattern of oogenesis of Callopora dumerilii
based on Silén ( 1945 ), he wrote that the oocyte enlarges in
the ovary, attaining a size of 120 μm, then ovulates into the
coelom where it continues to expand until it reaches 200 μm
Theoretically, such an increase might be achieved through
absorption of water, which is possibly the case for broadcasting species but there is no evidence in the literature that this
is also true for brooders.
One of the most valuable sources of the heterogenous
information concerning parental care in Bryozoa was published by Ström ( 1977 ) in a comprehensive review of brooding in the Gymnolaemata. Cheetham and Cook ( 1983 ) gave
a short review of brooding in Gymnolaemata in the Treatise
on Invertebrate Paleontology .
Several important papers on bryozoan sexual reproduction
were published in the 1980s. Nielsen ( 1981 ) undertook a complex study, working on Pacifi cincola insculpta (as
‘ Hippodiplosia ’) and Fenestrulina miramara (as F . malusii ).
He recorded the duration of synchronized events, including
oocyte growth, oviposition and embryo development in
repeated succession. In gonochoristic P . insculpta , maturation
of the fi rst oocyte ends with degeneration of the feeding polypide, which is replaced by a new dwarf, non-feeding one.
Oviposition, which lasts less than a minute, occurs beneath the
closed zooidal operculum, so the coelomopore was not
observed. The egg is only slightly deformed during its passage
to the ovicell, becoming about 2–3 times longer than its diameter. In F . miramara , oviposition is provided by the normal
protruded polypide, generally as described by Gerwerzhagen
( 1913 ) and Silén ( 1945 ). However, the actual transfer takes
place much faster than in other species, with the egg “suddenly squeezed through the pore into the ovicell almost without becoming deformed” (p. 114). In turn, this differs from
Appendices
seasons in particular and life cycles in general. Gordon
recognized three “breeding patterns” among 23 species of
New Zealand intertidal bryozoans, depending on the season
and duration of the reproductive activities. He also made an
attempt to classify their “brooding habits”. Interestingly, in
dissected ovicells of Macropora levinseni (as Macropora
grandis ), Gordon found 2–4 simultaneously brooding
embryos. Eggleston studied life cycles and reproductive patterns (terms and duration of reproductive season and colony
longevity), recording gonadal activity, brooding, spawning
and larval settlement in more than 50 species from the Isle of
Man. He divided them into four groups (those living less
than a year, annuals, biennials and perennials), depending on
colony longevity and the number of breeding/non-breeding
generations presented through the seasons. Interestingly,
Gautier ( 1962 ), who studied Mediterranean bryozoans,
found that seasonality is refl ected in reproduction to depths
of 20 m, whereas, at greater depths, the same species were
breeding for the most of the year. Eggleston ( 1972 ) showed
that the number of embryo-bearing zooids in the colony, the
size at which the colony starts reproduction, embryo size and
the rate of embryo development are related to the length of
the breeding season and colony longevity. In general, shorter
longevity means that a higher percentage of zooids brood,
their larvae are smaller and their development is faster. The
size at which the colony begins to reproduce is related to the
length of the breeding season and the longevity of the colony.
Most nearshore species have a short breeding period that is
probably connected with the variability of the shore environment. Eggleston also suggested that internally brooded
embryos are better protected against environmental variations, so internal brooders frequently occur in the upper
intertidal, where they are often exposed to drying. In
Bicellariella ciliata , Eggleston described sexual colony
zonation (sometimes repeated), and discovered external
brooding in the “membrane sacs” of Eucratea loricata along
with internal brooding of several embryos simultaneously in
Oshurkovia littoralis (as Umbonula ). Internal brooding in
this species was fi rst recorded by Hastings ( 1944 ), subsequently using the term “internal ovisac” (Hastings 1964 ).
Dudley ( 1973 ) observed reproduction in the cheilostome
Conopeum tenuissimum , recording the timing of gonad
appearance and the subsequent gamete release. Zooids in
this case are protandrous hermaphrodites, with the intertentacular organ developing after the fi rst polypide cycle.
Mawatari ( 1975 ) and Mawatari and Mawatari ( 1975 ) studied
a similar life cycle in Membranipora serrilamella . Zooids
are protandrous hermaphrodites. Testes develop just beneath
the lateral and proximal region of the membranous frontal
wall, whereas the ovary develops in the distal half of the
zooid [the wall is not specifi ed], and they recorded more than
40 ovulated eggs per zooid. Two or more eggs are usually
found in the intertentacular organ during their release.
Accidentally swallowed eggs are defaecated soon afterwards.
A fertilization envelope is formed after the liberation of the
zygote, which transforms from a fl attened circular disk to a
sphere with a diameter about half the size of the disk.
Interestingly, despite their numerous observations, they
failed to observe polar bodies, suggesting that these break
away and degrade at an early stage in this species.
Ryland ( 1970 , 1974 , 1976 , 1982 ) reviewed sexual reproduction in Bryozoa, including all major discoveries made
subsequent to Hyman ( 1959 ) and identifying the most important unsolved problems. Ryland ( 1976 ) characterized in
detail three reproductive patterns outlined by Harmer ( 1926 )
and Woollacott and Zimmer ( 1975 ), and suggested that byproducts from the degenerated polypide could be used for
extraembryonic nutrition. Among the most interesting of
Ryland’s conclusions based on Marcus’s ( 1938a ) fi ndings is
that there are different methods of brooding, with or without
placental nutrition, among related groups, sometimes within
the same genus. He also usefully summarised available data
on the increase in larval volume during placental brooding.
Describing the pattern of oogenesis of Callopora dumerilii
based on Silén ( 1945 ), he wrote that the oocyte enlarges in
the ovary, attaining a size of 120 μm, then ovulates into the
coelom where it continues to expand until it reaches 200 μm
Theoretically, such an increase might be achieved through
absorption of water, which is possibly the case for broadcasting species but there is no evidence in the literature that this
is also true for brooders.
One of the most valuable sources of the heterogenous
information concerning parental care in Bryozoa was published by Ström ( 1977 ) in a comprehensive review of brooding in the Gymnolaemata. Cheetham and Cook ( 1983 ) gave
a short review of brooding in Gymnolaemata in the Treatise
on Invertebrate Paleontology .
Several important papers on bryozoan sexual reproduction
were published in the 1980s. Nielsen ( 1981 ) undertook a complex study, working on Pacifi cincola insculpta (as
‘ Hippodiplosia ’) and Fenestrulina miramara (as F . malusii ).
He recorded the duration of synchronized events, including
oocyte growth, oviposition and embryo development in
repeated succession. In gonochoristic P . insculpta , maturation
of the fi rst oocyte ends with degeneration of the feeding polypide, which is replaced by a new dwarf, non-feeding one.
Oviposition, which lasts less than a minute, occurs beneath the
closed zooidal operculum, so the coelomopore was not
observed. The egg is only slightly deformed during its passage
to the ovicell, becoming about 2–3 times longer than its diameter. In F . miramara , oviposition is provided by the normal
protruded polypide, generally as described by Gerwerzhagen
( 1913 ) and Silén ( 1945 ). However, the actual transfer takes
place much faster than in other species, with the egg “suddenly squeezed through the pore into the ovicell almost without becoming deformed” (p. 114). In turn, this differs from
Appendices