Dear Questionman,
 
Two interesting observations come to mind:
 
Firstly on the subject of shell aberrations being associated with a
selective disadvantage for mollusk within:  I once "dissected" a stranded
egg-case of Busycotypus canaliculatus (Linnaeus, 1758) and counted about 800
(dead, dried) embryos.  Three had sinistral shells.  The late Bob Wagner had
a similar experience in an (unpublished) experiment with the same species.
The frequency of reversed B. canaliculatus adults is much, much lower, I
only know of two shells (among perhaps hundreds of thousands) - both
accounted for by Paul Monfils.  I think it is safe to conclude that the
sinistral condition Bob and I observed was mighty sublethal.
 
As regards shell-less mollusks:  There are a few reports of sinistral (soft
parts anatomically reversed) adult pulmonate slugs - just like their
healthy-appearing testaceous relatives.
 
Harry
 
 
At 06:15 AM 3/26/99 -0800, you wrote:
>"Welcome back, Question Man!"
>Thanks. nice to BE back.
>        I guess we've all seen two headed snakes and six footed calves. The
>question is whether abberations in mollusks appear. We know that there
>are "freaks" among shells. These are usually exterior and may have
>nothing to do with the animal.
>        It would be a guess that if abberations do appear, that they would be
>wiped out in the juvenile stage, never growing to adulthood. Still the
>malacologists among you may know of and be able to describe some chance
>survivals among "freak" mollusks. Perhaps among the shell-less
>mollusks---.
>        The Question Man
>
Harry G. Lee
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