Big Black Crab

[Ruth]

Yikes - I just saw this guy in my tank. He is black and about 1 inch plus across on his body - front legs are smooth and shiney and other legs are hairy. I don't know if he's bad or not but I want him out. This is the first time I have seen him so I am not going to be able to just grab him - besides my tank is too big and too much rock. What is the best way to trap a crab without catching any fish? I doubt very much that I will be able to get a picture before I catch him to help with ID but will take one if I am successful with trapping. Please help