Looks an awful lot like a crab to me, not a pistol shrimp? But I dunno, my eyes are old and I've been needing glasses since grade 5 so maybe I'm seeing it wrong.
I have mixed feelings about rock crabs. On the one hand, they are a sign of healthy rock. On the other hand, anything with claws is untrustworthy (it's just that there are varying degrees of untrustworthiness). Having said that, I have a few in my cube tank that are too hard to do anything about (would have to take down the whole rock structure), they've been in there for years, no idea how they stay alive but they don't seem to be the cause of any wonton mayhem or such.. the last one I saw a few weeks ago had gotten huuuuuge. It's sort of annoying because the rock came to me dry, and I closely inspected each and every rock before putting in .. didn't find a thing. They just materialized months later. It's kind of a neat trick if you think of it.
