Flatworms are soft-bodied invertebrates. They have no respiratory organs; the flat shape allows oxygen to pass through their bodies by diffusion. Many flatworm species are hermaphroditic, which means that each individual is able to function as either a male or female.
Over half of the number of flatworm species are parasites that can cause harm to humans and livestock when digested. The flatworms on the reefs, however, are harmless and a joy to find.