Great thread! (always a good idea to dress up the list in new threads now and
then...). I have't seen anything too wierd growing on a mollusc, but our
Placopecten magellanicus Gmelin up here sure harbours a lot of variety on its
ofter-broad back - an old one can be its own mini-ecosystem!  A student at
Memorial U. in Newfoundland did an honors thesis on the topic of Placopecten
epiphytes, and in the process found one with 19 live species living on it,
representing 13 genera and 7 or 8 families of flora and fauna - now THAT's what
i call a mobile home!!

Cheers,
Ross.