The flatworms, known in scientific literature as Platyhelminthes (from the Greek πλατύ, platy, meaning "flat" and ἕλμινς (root: ἑλμινθ-), helminth-, meaning worm) are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals. Unlike other bilaterians they've no body cavity, and no specialized circulatory and respiratory organs, which restricts them to flattened shapes that allow… (More on Platyhelminthes)