CHAPTER 8
PARASITES OF COMMERCIALLY IMPORTANT
MARINE MOLLUSCS
THE PHYLUM MOLLUSCA
I. Phylum MOLLUSCA
Several species of molluscs belonging to the family Pyramidellidae
have been reported as parasites of commercially important marine
molluscs. It is the general opinion that more undoubtedly will be found,
but progress relative to these parasites has been comparatively slow,
the prime reason being that the taxonomy of these gastropods is
in such a state that it has discouraged many from working with this
group. Their very small sizes undoubtedly have also discouraged
some. The pyramidellids are all parasites, with molluscs and annelids
being the most common hosts. Others have been reported as parasites of poriferans, cnidarians, sipunculids, crustaceans, echinoderms,
hemichordates and tunicates (Robertson and Orr, 1961). Although
Laserson (1951, 1959), Sanders (1958) and Robertson and Orr (1961)
have suggested that certain pyramidellids may not be parasites since
they have been found free on piles, in cracks, under stones and rocks
and on algae, Ankel and Christensen (1963) have pointed out that the
majority of the species often do leave their hosts between feedings,
and hence are found detached and free-living. Indeed, the majority of
pyramidellids have been found detached from their hosts. Another
argument raised by Sanders (1958) in favor of his belief that Turbonilla
is not a parasite is that from his benthic samples taken in Buzzards
Bay, Massachusetts, he found possible hosts in insufficient numbers to
account for the numbers of Turbonilla found in the bottom communities. But, as Robertson and Orr (1961) and Ankel and Christensen
(1963) have correctly pointed out, Sanders inferred that Turbonilla
is host-specific. This need not be the case and hence Turbonilla, during
its parasitic phases, could feed on many of the species of molluscs, or
even other invertebrates, present. Furthermore, the specialization
portrayed by the gut of pyramidellids strongly suggests that they are
fluid feeders, thus they are dependent on the body fluids of hosts for
nutrition.
278
PARASITES OF COMMERCIALLY IMPORTANT
MARINE MOLLUSCS
THE PHYLUM MOLLUSCA
I. Phylum MOLLUSCA
Several species of molluscs belonging to the family Pyramidellidae
have been reported as parasites of commercially important marine
molluscs. It is the general opinion that more undoubtedly will be found,
but progress relative to these parasites has been comparatively slow,
the prime reason being that the taxonomy of these gastropods is
in such a state that it has discouraged many from working with this
group. Their very small sizes undoubtedly have also discouraged
some. The pyramidellids are all parasites, with molluscs and annelids
being the most common hosts. Others have been reported as parasites of poriferans, cnidarians, sipunculids, crustaceans, echinoderms,
hemichordates and tunicates (Robertson and Orr, 1961). Although
Laserson (1951, 1959), Sanders (1958) and Robertson and Orr (1961)
have suggested that certain pyramidellids may not be parasites since
they have been found free on piles, in cracks, under stones and rocks
and on algae, Ankel and Christensen (1963) have pointed out that the
majority of the species often do leave their hosts between feedings,
and hence are found detached and free-living. Indeed, the majority of
pyramidellids have been found detached from their hosts. Another
argument raised by Sanders (1958) in favor of his belief that Turbonilla
is not a parasite is that from his benthic samples taken in Buzzards
Bay, Massachusetts, he found possible hosts in insufficient numbers to
account for the numbers of Turbonilla found in the bottom communities. But, as Robertson and Orr (1961) and Ankel and Christensen
(1963) have correctly pointed out, Sanders inferred that Turbonilla
is host-specific. This need not be the case and hence Turbonilla, during
its parasitic phases, could feed on many of the species of molluscs, or
even other invertebrates, present. Furthermore, the specialization
portrayed by the gut of pyramidellids strongly suggests that they are
fluid feeders, thus they are dependent on the body fluids of hosts for
nutrition.
278