It's an emerald crab. About the size of a quarter. Eats bubble algae and other algae. I don't like having crabs/shrimp in my tank. These guys cost 8$ at Cali Reef Co. Anybody want him? He will be donated to a Local Fish Store if no one wants him. Located in San Mateo. Will be heading to Neptune Aquatics in San Jose today 3/21/2015 if you want to meet and pick him up.