xvii
Moreover, some molecular data (Halanych et al. 1995; Halanych 1996; Mackey et al. 1996;
Winnepenninckx et al. 1998; Giribet et al. 2009; Peterson and Eernisse 2001; Helmkampf
et al. 2008a; Mallatt et al. 2010, 2012) indicate bryozoans as basal to the Phoronida–
Brachiopoda “group”, which, though hypothetically possible, does not correspond to paleontological data (Conway Morris et al. 1996; see also Cohen and Gawthrop 1996; Zrzavý et al.
1998; Halanych 2004). In contrast, Dewel et al. (2002) united phoronids and brachiopods,
placing them in a position basal to Bryozoa, while in the analysis by Hejnol et al. (2009) these
three spiralian groups are distant to each other, with Phoronida being the basal-most. In the
multigene analysis of Helmkampf et al. (2008b), bryozoans and phoronids (to the inclusion of
annelids) form a monophyletic group, while brachiopods were considered basal to them;
although nodal support was low for these inferences. On the other hand, Bourlat et al. (2008)
united bryozoans and brachiopods without making any connection to the phoronids. Analysis
of complete mitochondrial genomes made by Jang and Hwang (2009) showed bryozoans
forming a monophyletic clade with brachiopods, while the sister group to the phoronids was
unresolved. Conversely, analyses of the mitochondrial protein-coding genes at the amino acid
level by Sun et al. (2009, 2011), Shen et al. (2012) and Waeschenbach et al. (2006) resolved
chaetognaths to be the sister group to Bryozoa, a fi nding which is likely to be the result of longbranch attraction. Nesnidal et al. (2011, p. 1) demonstrated that “the relationships of the
lophophorate lineages within Lophotrochozoa differ strongly depending on the data set and the
used method”. Earlier Jenner and Littlewood (2008, p. 1508) wrote in this context: “Taxa such
as … Ectoprocta behave like phylogenetic renegades, residing in as many different clades as
there are studies”, whereas Hejnol (2010) pointed to the problem of the phylogenetic placement of the Polyzoa (Ectoprocta + [Entoprocta + Cycliophora]) within Spiralia (see also
Nielsen 2012). Thus, at the moment we can only state that lophotrochozoan affi nities are well
supported for these three groups, but much more research is needed to reveal their exact
position.
The evolution of views on the origination sequence of different bryozoan groups and their
phylogenetic relations can be summarized as follows. Phylum Bryozoa comprises three
classes: Stenolaemata (exclusively marine bryozoans), Gymnolaemata (mostly marine, rarely
brackish-water and freshwater bryozoans) and Phylactolaemata (exclusively freshwater bryozoans). According to early hypotheses, Phylactolaemata, which shares greatest morphological
similarity with the phoronids, is the most ancient bryozoan group (Caldwell 1882; Korschelt
and Heider 1893, see also Hyman 1959 for discussion), Gymnolaemata is derived from the
Phylactolaemata (Gerwerzhagen 1913) (i.e. phylactolaemates are paraphyletic, and the ancient
phylactolaemates are the stem group for gymnolaemates), and gymnolaemates and stenolaemates share a common ancestor (“ancestral Gymnolaemata”) that originated from the ancient
phylactolaemates (Jebram 1973, 1986). Although not mentioning a common ancestor, Silén
(1944) speculated that phylactolaemates and stenolaemates originated from an ancestral form
with a primitive colonial structure and that gymnolaemates (“Cheilo-Ctenostomata”) could
have evolved from ancient Phylactolaemata. A diametrically opposed viewpoint is that
Phylactolaemata is the most derived group, originating from the more primitive marine gymnolaemate (ctenostome) bryozoans (Schneider 1869; Kraepelin 1887; Marcus 1924; Bassler
1953). Borg (1926) suggested that all three bryozoan classes were independent lineages that
evolved from the common ancestral group “Pro-bryozoa”, with phylactolaemates and stenolaemates being somewhat more closely related to each other than to gymnolaemates (see also
Silén 1942, 1944; Hyman 1959). Lemche (1963) derived marine bryozoans from early phoronids, and, curiously, freshwater bryozoans from the “Prae-Rhizostomeae” (rhizostome medusae). Yet another hypothesis allows the possibility that marine and freshwater bryozoans
evolved independently from different phoronid-like ancestors, while stenolaemates evolved
from Gymnolaemata (Mundy et al. 1981) (for additional discussion see also Larwood and
Taylor 1979; McKinney and Jackson 1989; Todd 2000; Taylor and Ernst 2004; Wood and Lore
2005; Ernst and Schäfer 2006; Hausdorf et al. 2010). It should be noted that some molecular
studies question the monophyly of bryozoans (Cohen and Gawthrop 1996; Helmkampf et al.
Introduction
Moreover, some molecular data (Halanych et al. 1995; Halanych 1996; Mackey et al. 1996;
Winnepenninckx et al. 1998; Giribet et al. 2009; Peterson and Eernisse 2001; Helmkampf
et al. 2008a; Mallatt et al. 2010, 2012) indicate bryozoans as basal to the Phoronida–
Brachiopoda “group”, which, though hypothetically possible, does not correspond to paleontological data (Conway Morris et al. 1996; see also Cohen and Gawthrop 1996; Zrzavý et al.
1998; Halanych 2004). In contrast, Dewel et al. (2002) united phoronids and brachiopods,
placing them in a position basal to Bryozoa, while in the analysis by Hejnol et al. (2009) these
three spiralian groups are distant to each other, with Phoronida being the basal-most. In the
multigene analysis of Helmkampf et al. (2008b), bryozoans and phoronids (to the inclusion of
annelids) form a monophyletic group, while brachiopods were considered basal to them;
although nodal support was low for these inferences. On the other hand, Bourlat et al. (2008)
united bryozoans and brachiopods without making any connection to the phoronids. Analysis
of complete mitochondrial genomes made by Jang and Hwang (2009) showed bryozoans
forming a monophyletic clade with brachiopods, while the sister group to the phoronids was
unresolved. Conversely, analyses of the mitochondrial protein-coding genes at the amino acid
level by Sun et al. (2009, 2011), Shen et al. (2012) and Waeschenbach et al. (2006) resolved
chaetognaths to be the sister group to Bryozoa, a fi nding which is likely to be the result of longbranch attraction. Nesnidal et al. (2011, p. 1) demonstrated that “the relationships of the
lophophorate lineages within Lophotrochozoa differ strongly depending on the data set and the
used method”. Earlier Jenner and Littlewood (2008, p. 1508) wrote in this context: “Taxa such
as … Ectoprocta behave like phylogenetic renegades, residing in as many different clades as
there are studies”, whereas Hejnol (2010) pointed to the problem of the phylogenetic placement of the Polyzoa (Ectoprocta + [Entoprocta + Cycliophora]) within Spiralia (see also
Nielsen 2012). Thus, at the moment we can only state that lophotrochozoan affi nities are well
supported for these three groups, but much more research is needed to reveal their exact
position.
The evolution of views on the origination sequence of different bryozoan groups and their
phylogenetic relations can be summarized as follows. Phylum Bryozoa comprises three
classes: Stenolaemata (exclusively marine bryozoans), Gymnolaemata (mostly marine, rarely
brackish-water and freshwater bryozoans) and Phylactolaemata (exclusively freshwater bryozoans). According to early hypotheses, Phylactolaemata, which shares greatest morphological
similarity with the phoronids, is the most ancient bryozoan group (Caldwell 1882; Korschelt
and Heider 1893, see also Hyman 1959 for discussion), Gymnolaemata is derived from the
Phylactolaemata (Gerwerzhagen 1913) (i.e. phylactolaemates are paraphyletic, and the ancient
phylactolaemates are the stem group for gymnolaemates), and gymnolaemates and stenolaemates share a common ancestor (“ancestral Gymnolaemata”) that originated from the ancient
phylactolaemates (Jebram 1973, 1986). Although not mentioning a common ancestor, Silén
(1944) speculated that phylactolaemates and stenolaemates originated from an ancestral form
with a primitive colonial structure and that gymnolaemates (“Cheilo-Ctenostomata”) could
have evolved from ancient Phylactolaemata. A diametrically opposed viewpoint is that
Phylactolaemata is the most derived group, originating from the more primitive marine gymnolaemate (ctenostome) bryozoans (Schneider 1869; Kraepelin 1887; Marcus 1924; Bassler
1953). Borg (1926) suggested that all three bryozoan classes were independent lineages that
evolved from the common ancestral group “Pro-bryozoa”, with phylactolaemates and stenolaemates being somewhat more closely related to each other than to gymnolaemates (see also
Silén 1942, 1944; Hyman 1959). Lemche (1963) derived marine bryozoans from early phoronids, and, curiously, freshwater bryozoans from the “Prae-Rhizostomeae” (rhizostome medusae). Yet another hypothesis allows the possibility that marine and freshwater bryozoans
evolved independently from different phoronid-like ancestors, while stenolaemates evolved
from Gymnolaemata (Mundy et al. 1981) (for additional discussion see also Larwood and
Taylor 1979; McKinney and Jackson 1989; Todd 2000; Taylor and Ernst 2004; Wood and Lore
2005; Ernst and Schäfer 2006; Hausdorf et al. 2010). It should be noted that some molecular
studies question the monophyly of bryozoans (Cohen and Gawthrop 1996; Helmkampf et al.
Introduction