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6.1 Introduction
Among mollusks, most parasites are gastropods. Weinstein and Kuris (2016) estimated that parasitism has evolved convergently at least nine times within Gastropoda
out of more than 200 times it evolved within Metazoa. Parasitic or carnivorous grazers more or less permanently attached to their hosts form some of the most diverse
living groups of gastropods. An origin of a parasitic lifestyle from carnivorous relatives seems to be a common prerequisite in metazoans, particularly in gastropods
(Takano and Kano 2014). Modern groups of parasitic gastropods belong to higher
gastropods (Apogastropoda) i.e., Caenogastropoda and Heterobranchia. However, I
am not aware of any living parasitic patellogastropods, vetigastropods or neritimorphs (Ponder and Lindberg 1997). The living gastropod family groups
Pyramidellidae, Eulimidae, Epitoniidae, Architectonicidae, Mathildidae,
Coralliophilinae, Aclididae, Pedicularidae, Caledoniellidae, Ovulidae, Triviidae,
Colubrariidae, Cypraeidae, Cancellariidae, Marginellidae and Pseudosacculidae are
considered to represent parasites in a strict sense or contain at least one or more
parasitic species (e.g., Warén 1983, p. 27, Table 6; Lorenz 2005, Table 5.5). Several
of the mentioned families contain few parasitic species and/or have a scarce fossil
record and are not considered here in depth.
Eulimidae feed on echinoderms and Pyramidellidae are ectoparasites feeding
on the body fluids of various invertebrates, especially polychaete worms and mollusks (e.g., Ankel 1949; Robertson and Mau-Lastovicka 1979). Epitoniidae
(Janthinoidea), Architectonicidae, Mathildidae and Ovulidae feed on Cnidaria
(anthozoans) either as parasites or as carnivorous grazers (e.g., Kohn 1983).
Coralliophilinae (Muricidae, Neogastropoda) live in and feed on corals. Robertson
(1970) concluded that adaptations for feeding on Cnidaria in unrelated gastropod
families include cuticularized esophaguses and proboscises, ptenoglossate-like radular teeth and total loss of radulae.
The majority of parasitic gastropods are small and high-spired with a generally
low shell morphological disparity within each of the families so that alpha taxonomy (species identification and discrimination) is usually very difficult. This also
limits the fossil record of parasitic gastropods: Small tiny, mostly aragonitic gastropod shells are rarely preserved at all or in sufficient quality for an identification,
especially in formations of high geological age (Paleozoic and Mesozoic) (cf.
Roden et al. 2019) (Table 6.1). However, there are also numerous examples in each
family where species and genera deviate strongly from the standard morphology so
that low disparity within families is not without exceptions. The high diversity of
some of these families can be interpreted as result of a pronounced host specificity
and co-evolution—but although plausible, this has yet to be demonstrated in detail.
Most species of the mentioned families are ectoparasites and are attached by mucous
threads or by the proboscis/snout to their hosts. Endoparasitism does occur but is
seemingly rare. However, direct observations on feeding and behavior are scarce in
relation to the vast diversity of these snails. Parasitic gastropods may have reduced
their radula or have adapted their radula for feeding on tissue of their host.
A. Nützel
6.1 Introduction
Among mollusks, most parasites are gastropods. Weinstein and Kuris (2016) estimated that parasitism has evolved convergently at least nine times within Gastropoda
out of more than 200 times it evolved within Metazoa. Parasitic or carnivorous grazers more or less permanently attached to their hosts form some of the most diverse
living groups of gastropods. An origin of a parasitic lifestyle from carnivorous relatives seems to be a common prerequisite in metazoans, particularly in gastropods
(Takano and Kano 2014). Modern groups of parasitic gastropods belong to higher
gastropods (Apogastropoda) i.e., Caenogastropoda and Heterobranchia. However, I
am not aware of any living parasitic patellogastropods, vetigastropods or neritimorphs (Ponder and Lindberg 1997). The living gastropod family groups
Pyramidellidae, Eulimidae, Epitoniidae, Architectonicidae, Mathildidae,
Coralliophilinae, Aclididae, Pedicularidae, Caledoniellidae, Ovulidae, Triviidae,
Colubrariidae, Cypraeidae, Cancellariidae, Marginellidae and Pseudosacculidae are
considered to represent parasites in a strict sense or contain at least one or more
parasitic species (e.g., Warén 1983, p. 27, Table 6; Lorenz 2005, Table 5.5). Several
of the mentioned families contain few parasitic species and/or have a scarce fossil
record and are not considered here in depth.
Eulimidae feed on echinoderms and Pyramidellidae are ectoparasites feeding
on the body fluids of various invertebrates, especially polychaete worms and mollusks (e.g., Ankel 1949; Robertson and Mau-Lastovicka 1979). Epitoniidae
(Janthinoidea), Architectonicidae, Mathildidae and Ovulidae feed on Cnidaria
(anthozoans) either as parasites or as carnivorous grazers (e.g., Kohn 1983).
Coralliophilinae (Muricidae, Neogastropoda) live in and feed on corals. Robertson
(1970) concluded that adaptations for feeding on Cnidaria in unrelated gastropod
families include cuticularized esophaguses and proboscises, ptenoglossate-like radular teeth and total loss of radulae.
The majority of parasitic gastropods are small and high-spired with a generally
low shell morphological disparity within each of the families so that alpha taxonomy (species identification and discrimination) is usually very difficult. This also
limits the fossil record of parasitic gastropods: Small tiny, mostly aragonitic gastropod shells are rarely preserved at all or in sufficient quality for an identification,
especially in formations of high geological age (Paleozoic and Mesozoic) (cf.
Roden et al. 2019) (Table 6.1). However, there are also numerous examples in each
family where species and genera deviate strongly from the standard morphology so
that low disparity within families is not without exceptions. The high diversity of
some of these families can be interpreted as result of a pronounced host specificity
and co-evolution—but although plausible, this has yet to be demonstrated in detail.
Most species of the mentioned families are ectoparasites and are attached by mucous
threads or by the proboscis/snout to their hosts. Endoparasitism does occur but is
seemingly rare. However, direct observations on feeding and behavior are scarce in
relation to the vast diversity of these snails. Parasitic gastropods may have reduced
their radula or have adapted their radula for feeding on tissue of their host.
A. Nützel