Cymothoa exigua cannot harm humans. It is a crustacean that attacks the tongue of certain species of fish, mostly snappers, drinking the fish's blood until the tongue withers away. At that point, Cymothoa exigua takes the place of the fish's tongue and lives parasitically off the fish's blood and mucus.
Little is known about the life cycle of Cymothoa exigua, since it is usually observed only when it has become a fish's prosthetic tongue. Other mouth-infesting crustacean females often mate while they are in the fish's mouth, using the sperm of males that live in the same fish's gills, so it is quite possible this is how Cymothoa exigua reproduce.