My first question would be, are you sure its not a molt, mine has eatin a molt before? If not I would also suspect that the shrimp died first and the anemone got lucky. Having a hard exoskeleton shrimp are not affected by the stings of the anemone. Unless it were to get him in the mouth or eye, but even at that it would not incapacitate it. And BTA's have the one of the mildest stings of anemone species.