Hitchhiker crab ID please

[Francesca Evans]

Hi there! I'm very new to this and we are just starting out with our first reef tank. All going well so far and this weekend we brought home a piece of live rock / coral with a sponge /mushroom thing on it (told you we were beginners!). I've noticed this really cute crab ducking in and out of a hole on the rock and was really excited - until I started reading about how this is usually a bad thing! He's tiny, only about 1cm wide leg span. He can't cause any trouble... Can he?! Pic is of his perfect little moult! Any help gratefully received

 

[Jay York]

From what I have read and learned from others, if they have black tipped claws they are usually Gorilla crabs. They can irritate and eat coral. I have spotted one in my tank but haven't notices any shenanigans yet. They sell traps for them or you can make them yourself out of plastic soda bottles.

 

[DaveK]

Yes, it's a gorilla crab. You want to get rid of it ASAP, since they grow quickly and will attack fish and other livestock. This isn't so much the crab's fault. They are feeders of opportunity and that's just what they do.

Some people will put them in the sump or refugium and leave them there. I prefer to remove them from the system.