this thread was resurrected from the dead
there are over 8000 species of pyram snails and not a whole lot of info on there feeding habits. for years the common wisdom was that they were obligate predators and that if you found them on clams they would only feed on clams, and the one on snails would only feed on snails. i looked around for a long time for documentation to back this up and could never find any. finely someone sent me a study that proves pyrams are not very picky in what they eat and will in fact switch from snails to clams.
http://www.biolbull.org/cgi/reprint/157/2/320