I might have a bad crab....soooo

[MikeP]

I saw a little crab under one of my SPS colonies after lights out. He is all black with kinda hairy legs and pointy pinchers. He's a little bigger than an acro crab (which I have many of). I attempted to catch him but failed He looks very much like this http://melevsreef.com/id/xanthid.jpg but after some googling I'm not so sure he is xanthid. Should I do everything possible to catch this guy? I have not noticed any damage to corals at all. Maybe he's not a danger or maybe just not big enough yet? I know the best bet is to catch and sump him. That's easier said than done. I'm hoping to hear from some people that have had experience with this type of crab. I'm not sure how stressed I should be about this

Thanks!