Black Fingered Mud crab
This is a Black Fingered Mud crab - Xanthid crab. He arrived on a coral when small, but had grown quickly. This guy is black in real life; this picture is misleading. His pinchers remind me of a Mithrax crab, but it has 'teeth' within the claws. Because he can't be trusted, he was transferred into my refugium where he'd be trouble-free. Xanthids are Not Reef-safe.