I have a hermit crab that killed a Margarita snail for its shell about a week ago. Then yesterday it was going after my Nassarius snail (had it pinned against a rock) until my 6 line wrasse stepped in. The wrasse would nip at the hermit and make it retract in its shell and every time the hermit would try to come out, the wrasse would pick at it. This was so funny. It was like the wrasse was protecting the Nassarius snail.
I had no idea that hermit crabs could get that large! Guess I will be putting it in the fuge very soon.