Metabenedeniella parva n. sp. is described from the marine teleost Diagramma pictum from Heron Island, Queensland, Australia. The type species of the genus, Metabenedeniella hoplognathi, is redescribed and the generic diagnosis emended. Metabenedeniella parva differs from M. hoplognathi in many respects: M. parva is smaller; in M. parva the accessory sclerites and anterior hamuli are of similar length, but the posterior hamuli are smaller, whereas in M. hoplognathi the accessory sclerites are longer than the anterior hamuli and the anterior and posterior hamuli are of similar length; in M. parva the anterior hamuli span the distance between accessory sclerites and posterior hamuli and the anterior hamuli overlap the posterior hamuli considerably, but in M. hoplognathi the anterior hamuli partially overlap the posterior hamuli and do not extend anteriorly to reach the accessory sclerites; a sclerite close to the common genital aperture in M. parva is absent from M. hoplognathi. The 2 species differ also in some of their soft body parts. Specimens reported previously from the gills of Plectorhynchus chaetodonoides off Okinawa, Japan as M. hoplognathi are considered to be M. parva. The discovery of M. parva from only the dorsal fin of D. pictum at Heron Island enhances the notion that some benedeniine monogeneans from the body surfaces of fish exhibit strong site specificity.