Not sure if this is a gorilla crab or not?
Thanks
Gorilla crabs are hairy...he doesn't look hairy.
It is a mithrax crab which includes species like the Emerald crab. As with nearly all crabs, they are reef safe for a while until the find out that algae doesnt taste as good as small fish. The older/larger they get, the less reef safe they can become.
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If you see that its dead remove it immediately. I had an emerald crab die and my tank water stank horribly for a few days. I had to do a water change to get things back to normal.