Can't tell from the picture, but, are his legs hairy? Was he a resident of the bottom or just fell out of an acro colony? If he is a bottom resident, hairy or not, then that crab with the black tip claws is a resounding absolutely NOT reef safe. Its hard to tell from the picture exactly, but, he looks like one of the most carnivourous killers of the rock crabs. Good only for a FOWLR in a predator tank if at all. The black tips can split open clams and oysters, even larger than themselves, just to give you some idea of their strength. Of course they eat them then. There is another like this that eats sps, skeleton and all. Not kidding here. Its usually a hitchhiker in an acro though and masquarades as if it was a true acro crab. It has hairy legs, if its that one.