PionosyllisMalmgren, 1867 is revised based on a cladistic analysis of the 41 species considered herein as valid, two newly described species in this paper (Basidiosyllis victoriaeandOpisthodonta russelli), 11 species from other genera actually belonging, or related to,Pionosyllis, and 13 syllid species from different subfamilies. The phylogenetic analysis is based on 55 characters; a strict consensus of 1200 equally parsimonious trees (length = 314 steps) was obtained. The clades containing species usually included withinPionosyllisare newly named within the frame of a new Linnean classification of the group (except for one, belonging to another subfamily). The diagnosis ofPionosyllisis emended, and five new genera are proposed:Synmerosyllis,Basidiosyllis,Westheidesyllis,PerkinsyllisandBrevicirrosyllis.ParaehlersiaSan Martín, 2003, proved to be closely related toPionosyllis. Seven species are transferred toOpisthodontaLangerhans, 1879, here emended, and three transferred toNudisyllisKnox & Cameron, 1970 (according to San Martín & Hutchings, 2006).Opisthodonta uraga(Imajima, 1966) comb. nov. andPerkinsyllis longisetosacomb. nov. are redescribed.Pionosyllis compactaMalmgren, 1867,P. styliferaEhlers, 1913,P. giganteaMoore, 1908,P. enigmatica(Wesenberg-Lund, 1950), andNudisyllis magnidens(Day, 1953) comb. nov., are redescribed.Pionosyllis marquesensisMonro, 1939 andP. proceraHartman, 1965 likely belong to the Syllinae, thus they are not treated in the taxonomic account.