The status of all the species ascribed in the literature to Stylactaria is discussed, that nominal genus is considered a congener of Hydractinia and a new species (Hydractinia calderi n. sp.) is described. The medusae of the medusa-based genera Hansiella and Tregoubovia, formerly ascribed to the Hydractiniidae, are shown to be more like the medusae of Thecocodium, a genus having ptilocodiid hydroids. Both Hansiella and Tregoubovia are thus transferred to the Ptilocodiidae.With their removal from the Hydractiniidae, a redefinition of both families is provided. The genus Fiordlandia is considered as synonym of Clavactinia.