Examination of all species previously referred to the genus Hermadion revealed that the type species, H. magalhaensi Kinberg, 1856, is the only valid species in the genus. H. magalhaensi is redescribed and its synonymy with Hermadion longicirratus Kinberg, 1856, Hermadion kerguelensis McIntosh, 1885, and Lagisca laevis Hartmann-Schröder, 1962, is discussed. The generic attribution of 12 species that had already been moved from Hermadion to other genera by earlier authors is confirmed. Following our re-examination four species are moved to other genera: Harmothoe ornatus(Hartman, 1967) n. comb., Harmothoe africanus (Hartman, 1974) n. comb., Adyte hyalina (G.O. Sars, 1873) n. comb., and Neopolynoe acanellae (Verrill, 1881) n. comb., are redescribed. Due to lack of type material and insufficient descriptions Hermadion sabatieri Darboux, 1900, and H. fauveli Gravier, 1918 are considered indeterminable polynoids. Hermadion fugax Giard, 1890 is a nomen nudum, because a formal description has never been published. The generic diagnosis of Hermadion is emended and the validity of Hermadionella Uschakov, 1982 is confirmed. An identification key and synoptic tables of characters are provided for all genera considered here.