>Speaking of bryozoans (I think): I collected some weird dead things at
>minus tide at Fort Amador, Pacific Panama. Ranging from 5mm to 12mm they
>were vaguely reminiscent of Attiliosa nodulifera with small evenly spaced
>bumps, an oval aperture with sharp angles top & bottom, gastropod-like.
>They turned out to have various dead gastropods inside, but those were
>covered with a 2-3mm thickness of porous bryozoan-like material, including
>the bumps.
If the apertures were shaped like a capital "D", they probably were a
hermit crab-bryozoan symbiosis.  The bryozoan growing on the shell can
thoroughly obscure the shape of the original shell.  The hermit crab
doesn't have to keep finding new shells-the bryozoan grows along with it.
The "D" shape matches the shape of the crab.  Such symbioses are well-know
from the fossil record (with bryozoans, coral, or hydrozoans coating the
snail), but rarely documented from the Recent.
 
David Campbell