1
A. Ostrovsky, Evolution of Sexual Reproduction in Marine Invertebrates: Example of gymnolaemate bryozoans,
DOI 10.1007/978-94-007-7146-8_1, © Springer Science+Business Media Dordrecht 2013
Abstract
Chapter 1 is devoted to reproductive patterns in gymnolaemate bryozoans, especially
oogenesis, fertilization and brooding in the order Cheilostomata. Following a brief review
of the history of studies on cheilostome reproduction, the cell source, position and development of the gonads, sexual structure of colonies and fertilization are described, followed by
a detailed description and comparative analysis of the fi ve major reproductive patterns.
Correlations are demonstrated between the type of oogenesis (oligolecithal vs macrolecithal), ovary structure and type of embryonic incubation (non-placental vs placental).
Matrotrophy is far more common in Cheilostomata than previously realized, with placental
analogues being associated with the various brood- chamber types. Both incipient and substantial matrotrophy have been recorded. Sexual polymorphism, precocious fertilization,
nurse cells, coelomopores and oviposition are described from the literature and new data
and their evolution is discussed.
Keywords
Embryonic incubation • Evolution • Fertilization • Matrotrophy • Oogenesis • Sexual
polymorphism
Reproductive Patterns
of Gymnolaemate Bryozoa: General
Overview and Comparative Analysis
1
1.1
Brief Historical Overview of Studies
on Gymnolaemate Gonado- and
Gametogenesis and Fertilization
In the eighteenth and early nineteenth centuries, as the study
of Bryozoa was gaining momentum, understanding of their
sexual reproduction was poor, being represented by a few
passing and often obscure remarks in the descriptive
works of several early naturalists. After Ellis ( 1753 , 1755 )
described cheilostome brood chambers (ovicells) and
suggested (although in a confusing manner) that they were
connected with the production of eggs, Linnaeus ( 1758 ) and
Pallas ( 1766 ) wrote that these structures might be ovaries.
This opinion was widely accepted for almost a century,
although a number of observations indicated the erroneousness of this viewpoint (reviewed in Ostrovsky et al. 2008 ;
Ostrovsky 2009 ; see also Appendix I for detailed historical
analysis). Until the middle of the nineteenth century, as
Huxley ( 1856 , p. 191) wrote, even “the precise position of …
ovaria and testis has not been … determined”. At that time
phylactolaemates were chosen for studies more often than
marine bryozoans, probably because of their accessibility
and the transparency of the body wall. For instance, in the
“Polype à Panache” [phylactolaemate Lophopus crystallinus ,
the fi rst described living bryozoan], Trembley ( 1744 )
observed small spherical bodies moving with the cavity
fl uid from one zooid to another, and suggested that they were
eggs. Trembley also took statoblasts [dormant encapsulated
‘buds’] to be the same as eggs, since he observed the development of the fi rst polypide from them. [Statoblasts continued
to be considered as eggs even a century later (see Raspail
1828 ; Gervais 1837 ; Allman 1847 ; and references therein,
reviewed in Allman 1856 ; see also Cadée 2002 ).]
One of the fi rst detailed (and very precise) descriptions of
sexual reproduction in marine bryozoans was carried out by
Grant ( 1827 ), who also critically analyzed the observations
and ideas of previous authors such as Basteri ( 1762 ), Pallas
( 1766 ), Lamouroux ( 1816 ), and de Lamarck ( 1816 ). For a long
A. Ostrovsky, Evolution of Sexual Reproduction in Marine Invertebrates: Example of gymnolaemate bryozoans,
DOI 10.1007/978-94-007-7146-8_1, © Springer Science+Business Media Dordrecht 2013
Abstract
Chapter 1 is devoted to reproductive patterns in gymnolaemate bryozoans, especially
oogenesis, fertilization and brooding in the order Cheilostomata. Following a brief review
of the history of studies on cheilostome reproduction, the cell source, position and development of the gonads, sexual structure of colonies and fertilization are described, followed by
a detailed description and comparative analysis of the fi ve major reproductive patterns.
Correlations are demonstrated between the type of oogenesis (oligolecithal vs macrolecithal), ovary structure and type of embryonic incubation (non-placental vs placental).
Matrotrophy is far more common in Cheilostomata than previously realized, with placental
analogues being associated with the various brood- chamber types. Both incipient and substantial matrotrophy have been recorded. Sexual polymorphism, precocious fertilization,
nurse cells, coelomopores and oviposition are described from the literature and new data
and their evolution is discussed.
Keywords
Embryonic incubation • Evolution • Fertilization • Matrotrophy • Oogenesis • Sexual
polymorphism
Reproductive Patterns
of Gymnolaemate Bryozoa: General
Overview and Comparative Analysis
1
1.1
Brief Historical Overview of Studies
on Gymnolaemate Gonado- and
Gametogenesis and Fertilization
In the eighteenth and early nineteenth centuries, as the study
of Bryozoa was gaining momentum, understanding of their
sexual reproduction was poor, being represented by a few
passing and often obscure remarks in the descriptive
works of several early naturalists. After Ellis ( 1753 , 1755 )
described cheilostome brood chambers (ovicells) and
suggested (although in a confusing manner) that they were
connected with the production of eggs, Linnaeus ( 1758 ) and
Pallas ( 1766 ) wrote that these structures might be ovaries.
This opinion was widely accepted for almost a century,
although a number of observations indicated the erroneousness of this viewpoint (reviewed in Ostrovsky et al. 2008 ;
Ostrovsky 2009 ; see also Appendix I for detailed historical
analysis). Until the middle of the nineteenth century, as
Huxley ( 1856 , p. 191) wrote, even “the precise position of …
ovaria and testis has not been … determined”. At that time
phylactolaemates were chosen for studies more often than
marine bryozoans, probably because of their accessibility
and the transparency of the body wall. For instance, in the
“Polype à Panache” [phylactolaemate Lophopus crystallinus ,
the fi rst described living bryozoan], Trembley ( 1744 )
observed small spherical bodies moving with the cavity
fl uid from one zooid to another, and suggested that they were
eggs. Trembley also took statoblasts [dormant encapsulated
‘buds’] to be the same as eggs, since he observed the development of the fi rst polypide from them. [Statoblasts continued
to be considered as eggs even a century later (see Raspail
1828 ; Gervais 1837 ; Allman 1847 ; and references therein,
reviewed in Allman 1856 ; see also Cadée 2002 ).]
One of the fi rst detailed (and very precise) descriptions of
sexual reproduction in marine bryozoans was carried out by
Grant ( 1827 ), who also critically analyzed the observations
and ideas of previous authors such as Basteri ( 1762 ), Pallas
( 1766 ), Lamouroux ( 1816 ), and de Lamarck ( 1816 ). For a long