well..... i have no idea what that is....good job on catching it!

Those claws look like bad news to me.

I have one of those (or looks suspiciously like it) in my tank too. No damage seen on any of my corals (that looks crab related anyways, and I've had coral eating crabs so I can tell :razz:). I caught him eating algae the other day, no opportunity to spear him or anything, ahem I mean catch him and put him in a more appropriate environment :wink: I'm keeping an eye on him but so far I'm giving him the benefit of the doubt. However, if the opportunity arises he's a goner.

I had/have one like that too but more hair. I was aware of this guy for quite a while in my tank. Up till a few weeks ago he did not touch one single sps. One day I saw him snacking on a tricolor and a staghorn...so I caught and he lives in the fuge

Those claws look a lot like the claws of an emerald crab. To my eye, they look like they have flat pinching surfaces. If that is the case, this is likely a beneficial crab.