I just purchased some liverock from the LFS and when i got it home, and after a few days i noticed a crab looking creature under the rock. I was trying to do some research and it looks like a fiddler crab. Not sure if it is safe for my reef tank or not. I think he is the murderer of two of my hermit crabs. He seems to come out and then vanish when i come around. He's the size of a large hermit crab and only have one big claw on his right side. he has some hairly looking things on his legs and body. It looks like he has already shed one exoskeleton. Its creeping me out because i never see him, but i don't kno if its a hazard or not. Does anyone know what he might be?