Numbers and measurements have always interested me, although they do not
have a lot of signifigance when taken out of their larger contexts.  At
any rate, i read that as of the mid-70s there were about 50,000 spp of
moluscs bearing shells, most gastropods, with about 20% bivalves.
However, it is estimated that more than 100,000 more spp are yet  to be
found in the deep sea, and if one cares to take a glance almost any
selection of micro-shells, there will be a surprising percentage of
undescribed spp there, especially amoungst the "terrible Turridae"!!  An
illustration of  how poorly the fauna of even the more popular and
well-known areas really is, i will tell you about a friend's  quest to
find all spp possible just on the southern shore of Grand Bahama Island.
(late 70s- early 80s)- he and another person (whose name i cannot
remember- either of them, actually!!) found about 1100 spp in shallow
and brackish water alone, without really going after the bivalves much.
Of these, they  ultimately found that about 300+ were "unknown to
science"!!!  So, when all the chips are finally down, a total of 200,000
or more shell-bearing mollusc spp probably exist on the planet.  So far
as i know, the most comprehensive collection belongs to the
Smithstonian, which has 40,000++ spp, while wealthy, numbers-oriented
private collectors can pile up 25- 30,000 or so without too much
trouble, but of course have a hard time getting the deep-H2O critters.
The most highly populated family is undoubtedly Turridae, with perhaps
15% of the grand total, i think- although recently there have been
proposals to split up the family:  Can anyone summarize these
developments for all of us? (or correct/refine my numbers, and perhaps
epound a bit upon the non shell-toting side of the mollusc world as well
(numerically-speaking,ie!))
                                                                                                        -Ross from the Great White.