I think we have to look at the defense mechanisms of the other species in
question as well the foraging habits of the LOCAL predators.
 
Kurt
 
At 02:33 PM 1/26/98 -0500, you wrote:
>Protection from being swallowed does seem an obvious explanation for
>the various types of armament seen on gastropod shells, but - if that
>is the reason for such projections then:
>1.  Why are such projections so rare in bivalves?
>2.  Why are spines and flutes found primarily on those bivalves that
>are LEAST likely to be swallowed (sessile types like Spondylus,
>massive types like Tridacna)?
>3.  Why don't non-spiny gastropods living in the same habitat with
>the spiny types get wiped out by predators through selective
>predation (Murex capucinus among Murex cichoreus for example, or
>Murex trunculus among Murex brandaris).  Do the "smoothies" have some
>other, equally effective form of protection?
>4.  Why are various modern gastropods (Cypraeidae, Strombidae, etc.)
>LESS spiny than their extinct ancestors?
>Too tired to proffer any possible answers today, so thought I'd just
>toss a few more questions into the fray.
>
>Paul M.
>