Previous studies suggest that the polychaete taxa Hesionidae and Chrysopetalidae may not represent separate groups, that Pilargidae constitute a subgroup within Hesionidae, and that Hesionides and Microphthalmus are highly derived hesionids. Phylogenetic systematic analyses of Phyllodocida and the subgroup Nereidiformia are presented in order to clarify the position and delineation of these taxa. The phyllodocida analysis includes 18 families representing the majority of the taxa in the group, is rooted with Onuphidae, and is based on 42 absent; present coded morphological characters, obtained mainly from literature. All 69 resulting shortest trees include the clade (Chrysopetalidae, Nereididae, Hesionidae), but with either Syllidae, Nautiliniellidae, Pilargidae or (Aphroditiformia, Pisionidae) as sister. In- and outgroup taxon selection for the Nereidiformia study is dictated by the outcome of Phyllodocida analysis, with scores based on examined species of two chrysopetalids, four hesionids, one nereid, one pilargid, one pisionid, one syllid, plus the putative hesionids Hesionides arenaria and Microphthalmus sp. It is based on 46 absent; present coded morphological characters. Two equally parsimonious trees indicate that chrysopetalids and hesionids are well delineated, that pilargids and hesionids are non-overlapping, and that Microphthalmus and Hesionides are not hesionids.
