Hi sorry to hear this. BUT i'm not surprised. I had a gorgeous Maxima clam once. for a few weeks nothing happened. and then one night I noticed a hermit on it, clipping it. I got in and moved it away. it got chewed up a bit by hermit and I was hoping it would recover. died the next day. Ever since then, I had been warning people about hermit crabs. they turn predator on soft corals shrooms, anemones and clams from time to time. yes one ate a flame nem too. since then, no more crabs in my tanks. snails will toss up your frags. and when they spawn, the whole tank gets milky. and there goes your day trying to do water change.
the only CUC I will use are the tiny spider starfish that usually comes as hitch hikers.