Hmmmm, I'm not expert, but it's going to be very difficult to ID from those pics :)
However, "Chocolate dipped claws" is a halmark of gorilla crabs, which do hitchike on TBS rock, and can be a problem. If that's what you have, you may want to set a trap and try to remove them. They can live in your sump if you're so inclined to keep it, but they do get large.