I bought 2 Derasa clams for two separate tanks. One seems to be doing fine (has color and the mantle is open). The other...gone. Just a little bit of tissue in the shell and the muscle that pulls it shut. I'm not sure if it was eaten. The tank only has a Mollie, turbo snail, bumblebee snail and coral in it right now. Plus, the natural detritus eaters like bristleworms. I read that those can be an issue but I don't know a tank that doesn't have them. Anyway, I'm super bummed. It was open and I could see the mantle last night.