xix
1975; Larwood and Taylor 1979; Cheetham and Cook 1983; Taylor and Larwood 1988, 1990;
Todd 2000). Stenolaemata, with their calcifi ed zooids, probably evolved from a ctenostome
ancestor in the Late Cambrian; molecular analysis showed sister relationships between
Stenolaemata and Gymnolaemata (see above). The explosive evolution of Stenolaemata
resulted in fi ve orders – Cyclostomata, Trepostomata, Cystoporata, Cryptostomata and
Fenestrata – which achieved a high taxonomic diversity and played an important role in the
benthic communities of Paleozoic seas (Taylor and Larwood 1990; Anstey and Pachut 1995;
Taylor and Ernst 2004). One of the contributing factors in the evolutionary success of
Stenolaemata might have been the origin of parental care. The existence of embryonic incubation was suggested by Dunaeva (1968) and Astrova (1978) for Trepostomata and by Buttler
(1991) for Cystoporata. Putative embryo incubation chambers are an important character in the
systematics of the order Fenestrata (Tavener-Smith 1966; Stratton 1975, 1981; Southwood
1985; Bancroft 1986, 1988; Morozova 2001; see also Ernst and Schäfer 2006).
Orders Cyclostomata, Trepostomata and, possibly, Cystoporata survived, though with
losses, the global Permian-Triassic extinction event, but, with the exception of Cyclostomata,
became extinct in the Triassic (Cryptostomata and Fenestrata disappeared in the Permian)
(Taylor and Larwood 1988; Taylor and Ernst 2008). In contrast, the diversity of cyclostome
bryozoans, previously far outshone by their more successful relatives, began to increase. The
cyclostome heyday was the second half of the Mesozoic (Taylor and Larwood 1990; Lidgard
et al. 1993; McKinney et al. 2001; McKinney and Taylor 2001).
There are several sound arguments in favour of the hypothesis that the Paleozoic cyclostomes became extinct without leaving any descendants, and a very similar group appeared in
the Triassic that survives to this day (Ernst and Schäfer 2006; Taylor and Ernst 2008). Whatever
the case, during the Late Cretaceous extinction, the Cyclostomata again sustained heavy losses
(Taylor and Larwood 1988, 1990; Boardman et al. 1983; McKinney et al. 2001). Nevertheless,
bryozoans from this order are rather common in present-day bottom communities. Again, as
with Paleozoic stenolaemates, embryonic incubation is considered a key factor in the progress
of the Mesozoic cyclostomes, whose incubation chambers (gonozooids) are known from the
Late Triassic onward (Taylor and Michalik 1991; Lidgard et al. 1993). Details of gonozooid
structure are important in the systematics of fossil and living cyclostomes (Borg 1926; Brood
1972; McKinney 1987; Schäfer 1991; Viskova 1992; Ostrovsky 1991, 1995, 1998a, b;
Ostrovsky and Taylor 1996).
In the Late Jurassic, the Ctenostomata gave rise to a new gymnolaemate order, the
Cheilostomata (Pohowsky 1973; Banta 1975; Taylor 1981, 1986a, 1988, 1990, 1994; Taylor
and Ernst 2008). In the Late Cretaceous, after 60 Ma of low diversity, cheilostomes went
through a phase of explosive radiation, quickly becoming the dominant bryozoan group and
retaining this position until the present day (Cheetham and Cook 1983; McKinney and Jackson
1989; Taylor 2000). Jebram (1992) considered cheilostomes to be polyphyletic, a possibility
discussed by some other authors (Taylor 1988; Todd 2000).
Cheilostomes are one of the most diverse and numerous groups of marine colonial epibionts. Represented by 150 families and more than 1,060 genera, they make up about 95% of the
diversity of Recent Bryozoa (Gordon 2012). Moreover, сheilostomes are among the most
abundant marine foulers: for instance, in the Antarctic they may cover up to 90% of all rocky
surfaces, achieving densities in 1,000s colonies per square meter and being inferior in biomass
only to sponges, annelids and ascidians (Ryland 1967, 1982; Hayward 1995; Barnes and
Brockington 2003). Able to colonize all possible substrata – hard and soft, moving and immobile – cheilostome bryozoans are a key component of biocenoses, providing ample shelter as
well as settlement and feeding substrata for other organisms (Ryland 1970, 1976; McKinney
and Jackson 1989; Hayward and Ryland 1998, 1999; Ryland 2005).
The evolutionary success of the Cheilostomata can be explained by high integration of
modules within the colony and the extreme morphological and physiological plasticity
underlying the most diverse forms of colonial growth coupled with the emergence of an astonishing morphological and functional diversity of zooids (polymorphism) (Hyman 1959;
Introduction
1975; Larwood and Taylor 1979; Cheetham and Cook 1983; Taylor and Larwood 1988, 1990;
Todd 2000). Stenolaemata, with their calcifi ed zooids, probably evolved from a ctenostome
ancestor in the Late Cambrian; molecular analysis showed sister relationships between
Stenolaemata and Gymnolaemata (see above). The explosive evolution of Stenolaemata
resulted in fi ve orders – Cyclostomata, Trepostomata, Cystoporata, Cryptostomata and
Fenestrata – which achieved a high taxonomic diversity and played an important role in the
benthic communities of Paleozoic seas (Taylor and Larwood 1990; Anstey and Pachut 1995;
Taylor and Ernst 2004). One of the contributing factors in the evolutionary success of
Stenolaemata might have been the origin of parental care. The existence of embryonic incubation was suggested by Dunaeva (1968) and Astrova (1978) for Trepostomata and by Buttler
(1991) for Cystoporata. Putative embryo incubation chambers are an important character in the
systematics of the order Fenestrata (Tavener-Smith 1966; Stratton 1975, 1981; Southwood
1985; Bancroft 1986, 1988; Morozova 2001; see also Ernst and Schäfer 2006).
Orders Cyclostomata, Trepostomata and, possibly, Cystoporata survived, though with
losses, the global Permian-Triassic extinction event, but, with the exception of Cyclostomata,
became extinct in the Triassic (Cryptostomata and Fenestrata disappeared in the Permian)
(Taylor and Larwood 1988; Taylor and Ernst 2008). In contrast, the diversity of cyclostome
bryozoans, previously far outshone by their more successful relatives, began to increase. The
cyclostome heyday was the second half of the Mesozoic (Taylor and Larwood 1990; Lidgard
et al. 1993; McKinney et al. 2001; McKinney and Taylor 2001).
There are several sound arguments in favour of the hypothesis that the Paleozoic cyclostomes became extinct without leaving any descendants, and a very similar group appeared in
the Triassic that survives to this day (Ernst and Schäfer 2006; Taylor and Ernst 2008). Whatever
the case, during the Late Cretaceous extinction, the Cyclostomata again sustained heavy losses
(Taylor and Larwood 1988, 1990; Boardman et al. 1983; McKinney et al. 2001). Nevertheless,
bryozoans from this order are rather common in present-day bottom communities. Again, as
with Paleozoic stenolaemates, embryonic incubation is considered a key factor in the progress
of the Mesozoic cyclostomes, whose incubation chambers (gonozooids) are known from the
Late Triassic onward (Taylor and Michalik 1991; Lidgard et al. 1993). Details of gonozooid
structure are important in the systematics of fossil and living cyclostomes (Borg 1926; Brood
1972; McKinney 1987; Schäfer 1991; Viskova 1992; Ostrovsky 1991, 1995, 1998a, b;
Ostrovsky and Taylor 1996).
In the Late Jurassic, the Ctenostomata gave rise to a new gymnolaemate order, the
Cheilostomata (Pohowsky 1973; Banta 1975; Taylor 1981, 1986a, 1988, 1990, 1994; Taylor
and Ernst 2008). In the Late Cretaceous, after 60 Ma of low diversity, cheilostomes went
through a phase of explosive radiation, quickly becoming the dominant bryozoan group and
retaining this position until the present day (Cheetham and Cook 1983; McKinney and Jackson
1989; Taylor 2000). Jebram (1992) considered cheilostomes to be polyphyletic, a possibility
discussed by some other authors (Taylor 1988; Todd 2000).
Cheilostomes are one of the most diverse and numerous groups of marine colonial epibionts. Represented by 150 families and more than 1,060 genera, they make up about 95% of the
diversity of Recent Bryozoa (Gordon 2012). Moreover, сheilostomes are among the most
abundant marine foulers: for instance, in the Antarctic they may cover up to 90% of all rocky
surfaces, achieving densities in 1,000s colonies per square meter and being inferior in biomass
only to sponges, annelids and ascidians (Ryland 1967, 1982; Hayward 1995; Barnes and
Brockington 2003). Able to colonize all possible substrata – hard and soft, moving and immobile – cheilostome bryozoans are a key component of biocenoses, providing ample shelter as
well as settlement and feeding substrata for other organisms (Ryland 1970, 1976; McKinney
and Jackson 1989; Hayward and Ryland 1998, 1999; Ryland 2005).
The evolutionary success of the Cheilostomata can be explained by high integration of
modules within the colony and the extreme morphological and physiological plasticity
underlying the most diverse forms of colonial growth coupled with the emergence of an astonishing morphological and functional diversity of zooids (polymorphism) (Hyman 1959;
Introduction