154
dispersal. Subsequently, firmer attachment on fish tissues was acquired, followed by
encapsulation of the larva within the host epithelium. This might have allowed for
the feeding on host tissues, but required developing resistance to the host’s immune
system, which might have further strengthened their association.
Keywords Bivalvia · Galeommatoidea · Unionida · Parasitism · Evolution
5.1 Introduction
Parasitism has evolved independently 223 times in nearly half of the generally recognized animal phyla. The majority (83%) of unique origins are today described at or
below the family level (Weinstein and Kuris 2016). Bivalves commonly are the commensals of other invertebrates (Boss 1965a). Although some authors indicate even a
symbiotic relationship between some bivalves and their hosts (e.g. some galeommatoid bivalves according to Boss 1965a; Goto et al. 2014, 2016), it is often difficult to
detect what benefit, if any, the host species get (Boss 1965a). On the other hand, possible damage of the host tissues or its skeleton, the influence on physiology or food
competition are commonly described (e.g. Meyers and Millemann 1977; Scott and
Risk 1988; Haag et al. 1993; Lafferty 1993; Strayer and Smith 1996; Ricciardi et al.
1998; Jansen et al. 2001; Dodd et al. 2006; Bagur et al. 2013; Poulter et al. 2018).
Nevertheless true parasitic associations seem to be rare in bivalves, with the exceptions
of the parasitising larvae characterizing members of the freshwater order Unionida
(obligate parasites; e.g. Bauer 2001a), and facultative parasitic associations described
for two species within the marine superfamily Galeommatoidea (members of which
are generally known to establish obligate commensal relations with their hosts; Goto
et al. 2007, 2012, 2018; Bristow et al. 2010a; Bhaduri et al. 2017; Fig. 5.1). Furthermore,
most of the known obligate commensal or parasitic bivalve species appear to have a
high degree of specificity to their hosts (Boss 1965a; Bauer 2001b; Sato et al. 2011;
Goto et al. 2012, 2018; Patterson 2018), however parasitic larvae of members of the
freshwater order Unionida are diverse in this aspect and some are highly specialized,
while the others often are able to utilize a broader host species range (Bauer 2001b).
5.1.1 Bivalves in Relations with Other Organisms
Bivalves often settle on the hard surfaces of other organisms, especially in soft bottom environments—commonly on the shells of the other mollusks, on alive and
dead corals or on the external skeletons of crustaceans (e.g. Bromley and Heinberg
2006). They commonly actively choose a living host individual, and their molts,
dead skeletons or empty shells (Merrill 1960; Morton 1972; Lewandowski 1976;
Morton 1988; Scott 1988; Kleemann 1996; Owada 2009; Li and O’Foighil 2012;
Fig. 5.1). They often co-inhabit burrows of other invertebrates (Morton 1972;
Mikkelsen and Bieler 1989; Morton and Scott 1989; Goto et al. 2011, 2018; Bhaduri
et al. 2017). Some commensal clams have strong host-habitat preference and settle
A. Skawina
dispersal. Subsequently, firmer attachment on fish tissues was acquired, followed by
encapsulation of the larva within the host epithelium. This might have allowed for
the feeding on host tissues, but required developing resistance to the host’s immune
system, which might have further strengthened their association.
Keywords Bivalvia · Galeommatoidea · Unionida · Parasitism · Evolution
5.1 Introduction
Parasitism has evolved independently 223 times in nearly half of the generally recognized animal phyla. The majority (83%) of unique origins are today described at or
below the family level (Weinstein and Kuris 2016). Bivalves commonly are the commensals of other invertebrates (Boss 1965a). Although some authors indicate even a
symbiotic relationship between some bivalves and their hosts (e.g. some galeommatoid bivalves according to Boss 1965a; Goto et al. 2014, 2016), it is often difficult to
detect what benefit, if any, the host species get (Boss 1965a). On the other hand, possible damage of the host tissues or its skeleton, the influence on physiology or food
competition are commonly described (e.g. Meyers and Millemann 1977; Scott and
Risk 1988; Haag et al. 1993; Lafferty 1993; Strayer and Smith 1996; Ricciardi et al.
1998; Jansen et al. 2001; Dodd et al. 2006; Bagur et al. 2013; Poulter et al. 2018).
Nevertheless true parasitic associations seem to be rare in bivalves, with the exceptions
of the parasitising larvae characterizing members of the freshwater order Unionida
(obligate parasites; e.g. Bauer 2001a), and facultative parasitic associations described
for two species within the marine superfamily Galeommatoidea (members of which
are generally known to establish obligate commensal relations with their hosts; Goto
et al. 2007, 2012, 2018; Bristow et al. 2010a; Bhaduri et al. 2017; Fig. 5.1). Furthermore,
most of the known obligate commensal or parasitic bivalve species appear to have a
high degree of specificity to their hosts (Boss 1965a; Bauer 2001b; Sato et al. 2011;
Goto et al. 2012, 2018; Patterson 2018), however parasitic larvae of members of the
freshwater order Unionida are diverse in this aspect and some are highly specialized,
while the others often are able to utilize a broader host species range (Bauer 2001b).
5.1.1 Bivalves in Relations with Other Organisms
Bivalves often settle on the hard surfaces of other organisms, especially in soft bottom environments—commonly on the shells of the other mollusks, on alive and
dead corals or on the external skeletons of crustaceans (e.g. Bromley and Heinberg
2006). They commonly actively choose a living host individual, and their molts,
dead skeletons or empty shells (Merrill 1960; Morton 1972; Lewandowski 1976;
Morton 1988; Scott 1988; Kleemann 1996; Owada 2009; Li and O’Foighil 2012;
Fig. 5.1). They often co-inhabit burrows of other invertebrates (Morton 1972;
Mikkelsen and Bieler 1989; Morton and Scott 1989; Goto et al. 2011, 2018; Bhaduri
et al. 2017). Some commensal clams have strong host-habitat preference and settle
A. Skawina