102
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
cavity of Nautilus, Lichomolgus is found on the gills of Sepia, and
Octopicola lives on the mantle of Octopus. These, like the other ectosymbiotic copepods of molluscs, are relatively unmodified. Histopathological alteration, if any, associated with these have also not been studied.
Copepod symbionts are not known from the remaining three classes
of molluscs, namely, Monoplacophora, Amphineura and Scaphopoda.
It is of interest to note that Humes (1958a) has stated that based
on our present knowledge, host-specificity among copepod symbionts of
molluscs is not very strict. Furthermore, freshwater molluscs have no
known copepod symbionts.
b. Endoparasitism
Under this category, pathological changes associated with intracellular parasitism, intercellular parasitism, alimentary tract, and for
convenience, parasitism of other organ systems, will be considered
separately.
Intracellular parasitism. Although pathological changes in vertebrates, especially mammals, associated with such intracellular parasites
as Plasmodium spp. have been studied extensively (see reviews by
Trager, 1960a)b ; Moulder, 1962), comparable studies on molluscs
harboring intracellular parasites are wanting. This is especially true
in the case of marine molluscs. A number of sporozoans are known to
parasitize cells of marine molluscs ; however, in almost every instance
investigations have been concerned with the morphology and life cycles
of these parasites and not with the associated pathological changes.
Most of the known parasites of marine
molluscs fall into this category, including the large number of trematodes which commonly are found in the intertubular spaces of their
hosts’ hepatopancreas.
Despite the wealth of helminth fauna known from marine molluscs,
few studies of pathological changes have been reported. Furthermore,
many of the studies have been primarily concerned with cellular
defense mechanisms, a topic already reviewed (Section 11, A, 2).
Among known studies, Sparks (1963) has reported on the effects of
the metacestode of Tylocephalum on Crassostrea virginica. He has
noted the presence of a fibrous cyst wall surrounding each larva situated
in the host’s Leydig tissues although he has stated :
Whether the cyst wall is produced by the helminth or the oyster is not known,
but it is assumed that the extensive cysts are the result of a fibrosis of the
host tissues in response to the invasion of the parasite.
He has further stated :
Intercellular parasitism.
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
cavity of Nautilus, Lichomolgus is found on the gills of Sepia, and
Octopicola lives on the mantle of Octopus. These, like the other ectosymbiotic copepods of molluscs, are relatively unmodified. Histopathological alteration, if any, associated with these have also not been studied.
Copepod symbionts are not known from the remaining three classes
of molluscs, namely, Monoplacophora, Amphineura and Scaphopoda.
It is of interest to note that Humes (1958a) has stated that based
on our present knowledge, host-specificity among copepod symbionts of
molluscs is not very strict. Furthermore, freshwater molluscs have no
known copepod symbionts.
b. Endoparasitism
Under this category, pathological changes associated with intracellular parasitism, intercellular parasitism, alimentary tract, and for
convenience, parasitism of other organ systems, will be considered
separately.
Intracellular parasitism. Although pathological changes in vertebrates, especially mammals, associated with such intracellular parasites
as Plasmodium spp. have been studied extensively (see reviews by
Trager, 1960a)b ; Moulder, 1962), comparable studies on molluscs
harboring intracellular parasites are wanting. This is especially true
in the case of marine molluscs. A number of sporozoans are known to
parasitize cells of marine molluscs ; however, in almost every instance
investigations have been concerned with the morphology and life cycles
of these parasites and not with the associated pathological changes.
Most of the known parasites of marine
molluscs fall into this category, including the large number of trematodes which commonly are found in the intertubular spaces of their
hosts’ hepatopancreas.
Despite the wealth of helminth fauna known from marine molluscs,
few studies of pathological changes have been reported. Furthermore,
many of the studies have been primarily concerned with cellular
defense mechanisms, a topic already reviewed (Section 11, A, 2).
Among known studies, Sparks (1963) has reported on the effects of
the metacestode of Tylocephalum on Crassostrea virginica. He has
noted the presence of a fibrous cyst wall surrounding each larva situated
in the host’s Leydig tissues although he has stated :
Whether the cyst wall is produced by the helminth or the oyster is not known,
but it is assumed that the extensive cysts are the result of a fibrosis of the
host tissues in response to the invasion of the parasite.
He has further stated :
Intercellular parasitism.