> A few people know but it happens with bivalves too - for example Miltha
> childreni. It has one of the valves flat - placing it down so the umbus is
> curved towards right. In a few cases (not so rare though), the umbus is
> curved to the left.

Two other versions of handedness in bivalves:

In most cementing species (chamids, oysters, plicatulids, etc.),
attachment is by one valve.  For most groups, the attaching valve is
consistent, but in some it is variable.

The hinge teeth differ in the left and right valve.  In some species,
the tooth arrangement is reversed in rare individuals.  At least one
species, "Alasmidonta" heterodon, has a dentition reversed from other
members of its family (hence the species epithet).


--
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"

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