Well, I'm not positive that his mantle was collapsed now (unless they can recover from it) but something was definitely wrong with him. He seems much better now. I'm still keeping him in a shallow container (just enough water to cover him. changed several times a day) and he's eating and pooping and moving around. Before he didn't seem to able to right himself. He'd come almost all the way out of his shell trying to get on his foot. I tried to assist him but he just kept rolling himself over. I finally dropped some food right on him and he ate with vigor. Since I've moved him to a shallow container he seems fine if a little lethargic. I guess I wait and see...