NemerteaPronunciation: /ˌnɛməˈtiːə, nɪˈməːtɪə/Definition of Nemertea noun Zoology a small phylum that comprises the ribbon worms. Origin:modern Latin (plural), from Greek Nēmertēs, the name of a sea nymphNemertea in other Oxford dictionaries Definition of Nemertea in the US English dictionary