xxi
of an external cuticle and a calcifi ed layer underlain (and formed) by a thin epithelium and loose
peritoneum. In some cheilostomes the frontal wall is not calcifi ed and, as parietal muscles
contract, it fl exes inwards, thus applying pressure to the coelomic fl uid and resulting in the
protrusion of the tentacular crown. In many cases, however, there is a frontal skeletal wall and
the parietal muscles are attached to the fl oor of a special compensatory sac (ascus) serving as the
hydrostatic apparatus. The polypide is retracted with the help of two retractor muscles and
the zooidal orifi ce is closed by a chitinized fold (operculum). The only ganglion is located near
the pharynx. The coelomic cavity is represented by two communicating parts: the main visceral
coelom and the lophophoral coelom (circular peripharyngeal canal with radiating tentacular
coeloms). The peritoneum of the body wall is connected with the peritoneal lining of the intestine by funicular strands, considered as homologues of blood vessels by Carle and Ruppert
(1983). The cavities of neighbouring zooids communicate by means of pores closed by the
specialized pore-cell complexes associated with funicular strands. Polypides are renewed in the
course of degeneration and regeneration cycles, and their remnants are either removed or kept
inside zooids as so-called brown bodies. There are no specialized excretory organs.
Bryozoan colonies are hermaphroditic, consisting of sterile and gonochoric and/or hermaphroditic zooids (Reed 1991; Ostrovsky 2009). The gonads are located either on the internal
surface of the cystid walls or on the gut. In both cases they are associated with funicular strands
or occur on the strands themselves. Fertilization is internal. Sperms are released into the environment via pores in the tentacle tips, and enter the maternal coelom via the intertentacular
organ or the supraneural coelomopore. In non-brooding species, planktotrophic larvae with a
cuticularized bivalve shell, known as cyphonautes larvae, are formed from the spawned eggs.
In brooding species, embryos develop to become endotrophic coronate larvae. It is worth noting that the non-feeding larvae of some gymnolaemate species have retained some features
characteristic of cyphonautes such as the shell and/or a rudimentary intestine. Cleavage is
complete, biradial, equal at early stages and unequal at later stages, asynchronous and nondetermined. Gastrulation is by invagination or by immersion of four cells of the presumptive
mesentoderm into the blastocoel (Zimmer and Woollacott 1977; Reed 1991; Temkin 1994,
1996; Mukai et al. 1997; Gruhl 2008, 2010). Depending on the species, larval production
either peaks in a certain season or is more or less even throughout the year (reviewed in Ryland
1967; Reed 1991; Seed and Hughes 1992).
Order Cheilostomata is subdivided into four suborders (Gordon 2012). The paraphyletic
suborder Malacostegina exhibits primitive zooidal morphology, planktotrophic larvae and no
parental care. Suborder Flustrina (=Neocheilostomina), considered to be monophyletic, comprises the overwhelming majority of brooding cheilostomes, except those in the suborders
Inovicellina and Scrupariina. A characteristic feature of all brooding bryozoans is endotrophic
larvae that develop in incubatory chambers. Malacostegina is considered as ancestral to brooding cheilostomes, but whether or not the other suborders are monophyletic remains an open
question (Taylor 1988).
The fi rst fi ndings of fossil cheilostomes are from the Late Jurassic (Taylor 1981, 1986a,
1994). During the Early Cretaceous this group had low taxonomic diversity, being represented
only by two families of Malacostegina, Electridae and Wawaliidae (summarized in Taylor
1986b; Ostrovsky et al. 2008). However, starting from the Middle Cretaceous, the Cheilostomata
entered a phase of rapid diversifi cation (Taylor 1988), which, alternating with periods of
extinction and gradual decline, continued for about 90 Ma (Voigt 1985; Taylor and Larwood
1988; Lidgard et al. 1993; Macleod et al. 1997; McKinney et al. 1998; Sepkoski et al. 2000;
Taylor 2000).
The fi rst evidence of parental care in the Cheilostomata, namely the presence of brood
chambers, is from the Late Albian (Cheetham 1954, 1975; Cheetham et al. 2006). This means
that the emergence of larval brooding shortly preceded the onset of the above-mentioned diversifi cation phase. Based on this evidence, Taylor (1988) suggested that the presence of brood
chambers in cheilostomes meant that their larvae had become non-feeding (lecithotrophic).
According to this idea, lecithotrophy would have enhanced speciation, triggering the subsequent dramatic radiation within the order. The transition to lecithotrophy must have greatly
Introduction
of an external cuticle and a calcifi ed layer underlain (and formed) by a thin epithelium and loose
peritoneum. In some cheilostomes the frontal wall is not calcifi ed and, as parietal muscles
contract, it fl exes inwards, thus applying pressure to the coelomic fl uid and resulting in the
protrusion of the tentacular crown. In many cases, however, there is a frontal skeletal wall and
the parietal muscles are attached to the fl oor of a special compensatory sac (ascus) serving as the
hydrostatic apparatus. The polypide is retracted with the help of two retractor muscles and
the zooidal orifi ce is closed by a chitinized fold (operculum). The only ganglion is located near
the pharynx. The coelomic cavity is represented by two communicating parts: the main visceral
coelom and the lophophoral coelom (circular peripharyngeal canal with radiating tentacular
coeloms). The peritoneum of the body wall is connected with the peritoneal lining of the intestine by funicular strands, considered as homologues of blood vessels by Carle and Ruppert
(1983). The cavities of neighbouring zooids communicate by means of pores closed by the
specialized pore-cell complexes associated with funicular strands. Polypides are renewed in the
course of degeneration and regeneration cycles, and their remnants are either removed or kept
inside zooids as so-called brown bodies. There are no specialized excretory organs.
Bryozoan colonies are hermaphroditic, consisting of sterile and gonochoric and/or hermaphroditic zooids (Reed 1991; Ostrovsky 2009). The gonads are located either on the internal
surface of the cystid walls or on the gut. In both cases they are associated with funicular strands
or occur on the strands themselves. Fertilization is internal. Sperms are released into the environment via pores in the tentacle tips, and enter the maternal coelom via the intertentacular
organ or the supraneural coelomopore. In non-brooding species, planktotrophic larvae with a
cuticularized bivalve shell, known as cyphonautes larvae, are formed from the spawned eggs.
In brooding species, embryos develop to become endotrophic coronate larvae. It is worth noting that the non-feeding larvae of some gymnolaemate species have retained some features
characteristic of cyphonautes such as the shell and/or a rudimentary intestine. Cleavage is
complete, biradial, equal at early stages and unequal at later stages, asynchronous and nondetermined. Gastrulation is by invagination or by immersion of four cells of the presumptive
mesentoderm into the blastocoel (Zimmer and Woollacott 1977; Reed 1991; Temkin 1994,
1996; Mukai et al. 1997; Gruhl 2008, 2010). Depending on the species, larval production
either peaks in a certain season or is more or less even throughout the year (reviewed in Ryland
1967; Reed 1991; Seed and Hughes 1992).
Order Cheilostomata is subdivided into four suborders (Gordon 2012). The paraphyletic
suborder Malacostegina exhibits primitive zooidal morphology, planktotrophic larvae and no
parental care. Suborder Flustrina (=Neocheilostomina), considered to be monophyletic, comprises the overwhelming majority of brooding cheilostomes, except those in the suborders
Inovicellina and Scrupariina. A characteristic feature of all brooding bryozoans is endotrophic
larvae that develop in incubatory chambers. Malacostegina is considered as ancestral to brooding cheilostomes, but whether or not the other suborders are monophyletic remains an open
question (Taylor 1988).
The fi rst fi ndings of fossil cheilostomes are from the Late Jurassic (Taylor 1981, 1986a,
1994). During the Early Cretaceous this group had low taxonomic diversity, being represented
only by two families of Malacostegina, Electridae and Wawaliidae (summarized in Taylor
1986b; Ostrovsky et al. 2008). However, starting from the Middle Cretaceous, the Cheilostomata
entered a phase of rapid diversifi cation (Taylor 1988), which, alternating with periods of
extinction and gradual decline, continued for about 90 Ma (Voigt 1985; Taylor and Larwood
1988; Lidgard et al. 1993; Macleod et al. 1997; McKinney et al. 1998; Sepkoski et al. 2000;
Taylor 2000).
The fi rst evidence of parental care in the Cheilostomata, namely the presence of brood
chambers, is from the Late Albian (Cheetham 1954, 1975; Cheetham et al. 2006). This means
that the emergence of larval brooding shortly preceded the onset of the above-mentioned diversifi cation phase. Based on this evidence, Taylor (1988) suggested that the presence of brood
chambers in cheilostomes meant that their larvae had become non-feeding (lecithotrophic).
According to this idea, lecithotrophy would have enhanced speciation, triggering the subsequent dramatic radiation within the order. The transition to lecithotrophy must have greatly
Introduction