Andy,

I have found nematodes, protozoa, trematodes, and mites in living
mollusks.  The latter are commonly encountered in banana slugs and a
variety of naiades.

At least from the anthropocentric viewpoint, the most important parasites
are the digenetic trematodes, which infect a mollusk, undergo an explosive
asexual proliferation, and then emerge and infect a vertebrate.  In the
second host these flatworms reproduce sexually, producing various levels of
disease (e.g. liver flukes of sheep, schistosomes of humans) and producing
a second generation of infective forms to again infect a mollusk for the
completion of the life cycle.

Monogenetic trematodes complete their life cycle by parasitizing mollusks
exclusively. One evolutionary scenario places these as ancestral to those
digenetic forms - possibly predating the rise of the vertebrates, and
pointing to one of the earliest forms of animal parasitism.

I feel I've trespassed into your (evolutionary) turf here.  Maybe I need a
little editing here.

Harry


At 10:26 AM 9/7/2004, you wrote:
>Andrew et al.,
>
> >as i remember largest leech ever found lives on whales! its about 25 cm
>(maybe more).
>
>Light dawns. In his decidedly pessimistic eco-novel "The End of the Dream"
>(1972), Philip Wylie described how shoals of big leeches, deprived of their
>usual cetacean hosts, erupted onto the land to devour the next best thing:
>humans. (They got as far up-river as Cincinnati, Art. The city of Flying
>Pigs was devoured in its sleep.) For years, I thought he made them up.
>Wylie's point was that the ecologic imbalances that people create can
>eventually destroy us without warning. What made his novel particularly
>engaging was how he described one disaster after another while the
>politicians and general population never learned a thing.
>
>Returning to the subject: What kinds of parasites attack mollusks?
>
>Cheers,
>Andrew
>
>Andrew K. Rindsberg

Harry G. Lee
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