Mithraculus sculptus (common names: Emerald crab, green clinging crab), is a species of crab native to the Caribbean Sea. It is often kept in marine aquariums to keep them clean, but the Emerald crab is known to attack and kill smaller tank mates then himself. The Emerald crab is nocturnal and hides most of the day in caves in reef rocks. But sometimes is active during the day.