Notentera ivanovi is a parasitic platyhelminth found in the gut of a polychaete, Nephthys ciliata. N. ivanovi has no mouth, pharynx, or intestine; the dorsal epidermis of adult animals forms a thick pad which is very similar to gut epithelia even at the light microscopic level. Structure of ciliary rootlets and dermal glands with peculiar striated secretion bodies point to close relationships with the Fecampiidae, though other important characters imply placing the genus Notentera in a separate family. In mature sperm of N. ivanovi, the axonemes are fully incorporated; they are directed from proximal to distal, as in the Neodermata. We argue that new family, Notenteridae, should be included in the taxon Fecampiida. We also suggest that all Plathelminthes with neodermatan type of spermiogenesis (Fecampiidae, Urastomidae, and Neodermata) form a monophyletic branch within the Plathelminthes Neoophora.