Diagnosis
Small holoplanktic forms with body elongated (often posteriorly incomplete). Prostomium rounded, without antennae; eyes dorsal, paired or absent; palps small. First two segments fused, with two pairs of small tentacular cirri. Following setigers (2–10) with reduced parapodia, dorsal and ventral cirri sometimes absent on setigers 1 and 2. Remaining setigers with parapodia with short dorsal and ventral cirri, long setal lobes and compound spinigers. Pharynx eversible, unarmed or with two falcate, strong mandibles. Pygidium rounded or plateshaped, ciliated, without appendages. All species with branched chromatophores, either intensely or weakly pigmented.
Remarks
While dealing with some taxonomic problems in other holoplanktic taxa, StøpBøwitz (1984) regarded the Pontodoridae, Iospilidae, and Lopadorrhynchidae, as pelagic families without “many difficult systematic problems”. Further, Tebble (1958) made an early warning against the cosmopolitan distribution of pelagic polychaetes by stating that “a correlation has been found to exist between the distribution of species and the movements of water masses”. However, the fragility and scarcity of specimens, together with shallow taxonomic descriptions, have hindered the clarification of the distributional status of many taxa of pelagic polychaetes, including the Iospilidae. StøpBowitz (1996) recognized three iospilid genera, Phalacrophorus Greeff, 1879, with two species (P. pictus Greeff, 1879 and P. u n i f o r m i s Reibisch, 1895), and two monotypic genera: Iospilus Viguier, 1886 (I. phalacroides Viguier, 1886), and Pariospilus Viguier, 1911 (P. affinis Viguier, 1911). The monotypic genus Iospilospis (I. antillensis) described by Augener (1922) was regarded as a synonym of P. u n i f o r m i s (Dales & Peter 1972). Three of these four known species of Iospilidae were recorded in the surveyed area.