The flatworms, known in scientific literature as Platyhelminthes (from the Greek ÀλαÄÃÂ, platy, meaning "flat" and ἕλμιν (root: ἑλμινθ-), helminth-, meaning worm) are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals. Unlike other bilaterians they have no body cavity, and no specialized circulatory and respiratory organs, which restricts them to flattened shapes that allow oxygen and nutrients to pass through their bodies by diffusion.
