What is he... (BIG PICTURE)

[RaceFaceR1]

Good Bad?

This is the best pic I could get before he went back in his hole...

Look towads the right near the bottom... you can see his hand/claw...

 

[hdtran]

Looks like a crab to me. I can't help you with genus/species (as there are about a gazillion crabs out thre), but looks like a small stone crab.

Reasonably harmless until he gets bigger, at which point, as an opportunistic scavenger, he will 'make his own opportunities' with your snails & larger critters.

 

[saltnmyeye]

from what i can tell, looks like an emarald crab he is reef safe if it is.