Yep, I think it is a gorilla crab.
GORILLA CRABS
You want to keep a lookout for Gorilla crabs (xanthid species). These pesky buggers are predators that can cause damage to your reef, eating anemones, clams, and anything else they can get their claws around. They might look cute when they're small, but it's just not worth putting them into the tank. If you really want to keep them, you could put them into your sump/fuge (if you have one).
The sure-fire way to spot one of these is to look for the black tips on their claws. As they get larger, they become quite "hairy" all over.
Bryan Tacker - North Austin ( 620 and Parmer )
110g RR > 2x250w SE XM 10k with 2x140w Super Atinic > Matt Sump / Fuge > Red Berlin Skimmer.