The Lettuce Nudibranch, Elysia diomedea also known as the Lettuce Sea Slug, is a well-equipped algae eater that gets energy from the photosynthetic algae it consumes. They will even take the chlorophyll from the algae and incorporate it into its own tissue. Its body is green and wavy very closely resembling a leaf of lettuce. 

They are best housed in tanks with plenty of live rock and away from aggressive species. The Lettuce Nudibranch will rid your tank of unwanted algae while being a fascinating organism to watch. Unlike some other sea slugs, the Lettuce Nudibranch is not aggressive and not poisonous making it a risk-free addition to any tank.