I have had this crab in my tank for about 2+ years now, first noticed him when he was about a dime in diameter. Now he's about a quarter size. Hope the pic is good enough, If not ill try to get some better pics. It's very skittish.
I'm not good with crabs, but do see here.
I generally dispose of any crab, except like Petrolisthes. Their big claws have got to be used for something, ay?
Although I'll give credit to some, as they eat algae off their cave entrance "to the bone".