I think that you would need to accept that every individual detail has been potentially lost through the long evolutionary history of the group, and that a mollusc is anything that can be traced back to a proto-mollusc, which can be defined as having a mantle, radula and foot.
Allen  Aigen
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---------- "Monfils, Paul" <[log in to unmask]> writes:

From: "Monfils, Paul" <[log in to unmask]>
To: [log in to unmask]
Subject: Re: Conchology 101 Question
Date: Mon, 9 Sep 2002 11:06:52 -0400

Bivalves don't have a radula, but I believe all mollusks have a mantle (even
though they don't all produce a shell) and a foot (even though it is
modified beyond recognition in cephalopods).

Paul M.



Allen Aigen
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