Something is chopping off my starfish arms!

[Norstar]

A few months ago, I lost a starfish to some creature that was systematically chopping its arms off one at a time. Now its happening to my other starfish. I have a few hermit crabs, tangs, nigger trigger, and a clown fish. Nothing that I would assume would enjoy chopping off starfish arms. In fact, the arms are not being eaten, just left behind. I usually happens in the middle of the night.

Any ideas?