CHAPTER 1
INTRODUCTION
Although the role of molluscs as hosts of zooparasites has been
known for over two centuries, ever since Swammerdam found the redial
stage of trematodes in a snail in 1737, it has only been in relatively
recent years that host-parasite relationships between molluscs and their
parasites have been studied in any detail, and even now a great deal
remains to be elucidated. Understandably it has been the freshwater
gastropods that have been most extensively studied, since it is among
these that are found those species which serve as intermediate hosts of
parasites of medical and veterinary importance. For example, the
relationships between Lymnaea spp. and Fasciola hepatica and that
between Australorbis gbbratus and Schistosoma mansoni are among the
most extensively investigated. During the last two decades, however,
interest has developed in the symbionts of marine molluscs. This
interest has developed along two distinct, although artificial, lines.
The interest in parasites has stemmed from the realization that parasitism of marine molluscs, especially the economically important species, ’
has far-reaching economic implications. The interest in other types of
associations involving marine molluscs, although long in existence, has
been accelerated as the result of the surge of interest in marine biology
and biological oceanography all over the world. I n the case of
economically and potentially important parasites, it has been primarily
the parasites of pelecypods, such as edible oysters, clams and mussels,
that have received concentrated attention. Even in investigations
concerned with fundamental problems manifested by marine symbioses,
of which molluscs represent one partner, it has been almost exclusively
the estuarine species that have been studied. Little is yet known about
the symbionts of and their relationships with deep-sea molluscs.
Although the latter part of this review is concerned with the parasites of commercially important marine molluscs, it should be
emphasized that the biology of zoosymbionts of marine molluscs,
irrespective of their economic or medical importance, has a great deal to
contribute to our understanding of the nature of symbiotic relationships and deserves increased attention. All too often in the past, and
still true to some extent, parasitologists have concerned themselves
primarily with medically and economically important parasites, thus
1
A.Dd.B.-5
2
INTRODUCTION
Although the role of molluscs as hosts of zooparasites has been
known for over two centuries, ever since Swammerdam found the redial
stage of trematodes in a snail in 1737, it has only been in relatively
recent years that host-parasite relationships between molluscs and their
parasites have been studied in any detail, and even now a great deal
remains to be elucidated. Understandably it has been the freshwater
gastropods that have been most extensively studied, since it is among
these that are found those species which serve as intermediate hosts of
parasites of medical and veterinary importance. For example, the
relationships between Lymnaea spp. and Fasciola hepatica and that
between Australorbis gbbratus and Schistosoma mansoni are among the
most extensively investigated. During the last two decades, however,
interest has developed in the symbionts of marine molluscs. This
interest has developed along two distinct, although artificial, lines.
The interest in parasites has stemmed from the realization that parasitism of marine molluscs, especially the economically important species, ’
has far-reaching economic implications. The interest in other types of
associations involving marine molluscs, although long in existence, has
been accelerated as the result of the surge of interest in marine biology
and biological oceanography all over the world. I n the case of
economically and potentially important parasites, it has been primarily
the parasites of pelecypods, such as edible oysters, clams and mussels,
that have received concentrated attention. Even in investigations
concerned with fundamental problems manifested by marine symbioses,
of which molluscs represent one partner, it has been almost exclusively
the estuarine species that have been studied. Little is yet known about
the symbionts of and their relationships with deep-sea molluscs.
Although the latter part of this review is concerned with the parasites of commercially important marine molluscs, it should be
emphasized that the biology of zoosymbionts of marine molluscs,
irrespective of their economic or medical importance, has a great deal to
contribute to our understanding of the nature of symbiotic relationships and deserves increased attention. All too often in the past, and
still true to some extent, parasitologists have concerned themselves
primarily with medically and economically important parasites, thus
1
A.Dd.B.-5
2