National Geographic : 1962 Jan
Star coral owes its delicate green beau ty to the algae that live within the pol yps and help them extract lime from the ocean. The coral that forms living reefs needs some sunlight for survival. Flour ishing within 90 feet of the surface, it usually does not grow below 150 feet, where light is too weak. Spiral-shaped feather-duster worm, living in a star coral, filters plankton swept past by the current.