Yep, I think it is a gorilla crab.

GORILLA CRABS

You want to keep a lookout for Gorilla crabs (xanthid species). These pesky buggers are predators that can cause damage to your reef, eating anemones, clams, and anything else they can get their claws around. They might look cute when they're small, but it's just not worth putting them into the tank. If you really want to keep them, you could put them into your sump/fuge (if you have one).

The sure-fire way to spot one of these is to look for the black tips on their claws. As they get larger, they become quite "hairy" all over.