The parasitic isopod genus Tylokepon is recorded for the first time from the Mariana Islands and Australia. Tylokeponmarianensis sp. n. is described from the Mariana Islands, infesting Thusaenysirami (Laurie, 1906). The holotype female differs from other known Tylokepon females by the tri-lobed projection on pereomere 6, almost smooth lateral plates and pleopods, shape of oostegite 1, and widely opened brood pouch. The host is first recorded for bearing bopyrids. The new record of T.bonnieri Stebbing, 1904 from Australia on the type host extends the range of this species from China and India. A table of localities and hosts and a key to all species of Tylokepon are provided.
Keywords: Bopyridae; Epicaridea; Tylokepon; new records; new species.