Is this a Black Emerald Crab?

Bought some LR from the LFS today and as I put the rock into the water, something black dropped off and scurried away.  It was pretty frickin' fast.  Later, I got a better look at it and it's a jet-black crab with big claws.  Started reading on the forums of nightmare crabs with red eyes that kill corals and fish and got really worried. 

Just found him clinging to the bottom of a rock near the top of the tank.  Picked it up, dumped it in a bucket, and flicked him into a clear plastic container for a better look. 

Now, I need your help on two fronts. 

1)  When I look at him, he does look like a black version of an emerald crab.  Bumpy top, hairy legs, suction cup-like pincers. Am I right?  If I'm wrong, then what is it?

2)  Given that I'd like to eventually have a reef tank, will he be ok for that?  In another thread, someone wrote about a black emerald crab attacking a feather duster.  I do have one of those.  I have another much smaller green emerald crab who came on another piece of LR a while ago.  He seems well behaved.  Any reason to believe that a black one would be any different?  Right now, I only have a few pulsing xenia frags, a small green polyp sarco, and a couple of little blue mushrooms.

Not letting him out of the container until I know what to do.

Here are some pics:

I would relegate him to the sump if I had one.  For now, he's going to stay in the ventilated container I've got him trapped in.  Once I get a HOB refugium (because I don't have room for a sump), he'll go in there.  Also contemplating giving him back to the LFS.  He's just not cute enough to keep around. 

Everything I've read indicates that 90% of the folks seem more than a touch cautious about Black Emeralds.  Only a couple have "non-dangerous" reviews.  The rest seem pretty damning.  Better reef-safe than sorry, right?

Sorry Jax, I would give him/her to you but I already returned it to the LFS.  The guy there agreed with the decision to not put it in a reef tank.  His opinion was that it probably wouldn't be dangerous to fish, but any corals would be a 50/50 chance of being a meal.