PlatyhelminthesPronunciation: /ˌplatɪhɛlˈmɪnθiːz/Definition of Platyhelminthes noun Zoology a phylum of invertebrates that comprises the flatworms. Origin:modern Latin (plural), from platy- 'flat' + Greek helminth 'worm'Platyhelminthes in other Oxford dictionaries Definition of Platyhelminthes in the US English dictionary