Earlier this evening I talked with Jay and I believe the little briareus is so small (1/2 inch mantle) that it's probably eating amphipods, which are plentiful in his tank. He's provided plenty of food in the form of small crabs and snails, too. His water parameters are fine, so that's not a problem.
I also made the same suggestion that Cuttlegirl makes - that he remove the fish, which is possible for him to do.
So, let's hope all is well.
Nancy