The genus Haplosyllides was considered as monotypic, with H. floridana as the only valid species. The present revision includes two more species in this genus: H. aberrans comb. nov. and H. ophiocomae sp. nov. Syllis (Haplosyllis) aberrans (from Vietnam) was considered a junior synonym of H. floridana (from the Caribbean). The finding of additional specimens from Vietnam and Indonesia, and the study of the type series, allowed us to redescribe H. aberrans comb. nov. on the basis of morphological, ecological and biogeographical characteristics. Haplosyllides aberrans comb. nov. differs from H. floridana in having posterior simple chaetae with tips twice as long, a pharyngeal tooth in all non-reproductive individuals, and the granules inside the dorsal cirri oval, elongated, and roughly distributed in longitudinal parallel rows. Haplosyllides ophiocomae sp. nov. was previously reported (as H. aberrans) from Puerto Rico. Although geographically close, it differs from H. floridana in having serration on the upper edge of the major teeth of simple chaetae, relatively shorter dorsal cirri, and a distinct mode of life. Haplosyllides floridana lives as an endosimbiont of Xetospongia muta, H. aberrans comb. nov. as a facultative parasite of Platycaris latirostris, and H. ophiocomae sp. nov. as a commensal of Ophiocoma pumila and other brittle stars. The meaning of these associations is discussed in light of the available information. The remaining records of “Haplosyllides aberrans” from the Marshall Islands (associated with corals of the genus Heliopora) and from Brazil (among corals and calcareous algae) are considered as doubtful.