Originally Posted by
Bonebrake
I don't know for sure, but I vote against the clam foot.
It's not actually the foot, which is the fleshy muscle the clam uses to position itselt and dig in the sand. It appears to be discarded byssus threads, which are the secretions from the byssal gland, located near the foot. The clam uses them to attach itself to rocks or other hard surfaces, and can release them if it is no longer happy with its location. The whole gland can be ripped out, too, if someone forcefully tries to move the clam. I think I used to have some pictures, I'll see if I can dig them out....
Edit: I couldn't find mine, but here's one I pulled off the web