Dear Jan,
though I cannot say to be mainly interested in bivalves, I collected
lots
of them, as you problably also did, on the Belgian coast, including all
the
fossil ones you will find there. I am also just typing all the data from
my
bivalve collection trays into my PC right now.
I think bivalves do not only occur throughout all the climate zones from
arctic to tropical, but also at all depths. I can remember having read
about bivalves living around deep-sea hydrothermal vents. Unfortunately,
such shells will rarely be seen in collections, material from deep-sea
dredgings could be found in some musea.

My favourite is one from the Mediterranean though: the Venerid species
Callista (gr: the beautiful) chione.
Greetings form Germany
Michael