Revision of the taxonomy of Polycirrus Grube, 1850 (Annelida: Terebellida: Polycirridae).
The large polychaete genus Polycirrus (Terebellida: Polycirridae) is revised based on a morphological study of the type material of most of the approximately 74 nominal species; 59 species, including a new species, P. coibensis n.sp., from the Pacific coast of Panama, are accepted as valid. All characters are reanalysed and discussed in the light of recent phylogenetic studies of terebellomorph taxa, and a standard set of characters is developed. Most of the 59 accepted species are redescribed and illustrations provided in order to facilitate future identifications of members of the genus. We designate a neotype for the type species of the genus, Polycirrus medusa Grube, 1850, and a lectotype for P. elisabethae McIntosh, 1915, in order to stabilize the concept and type locality of these taxa. A replacement name is proposed for Polycirrus kerguelensis McIntosh, 1885, which is a secondary junior homonym of Ereutho kergulenesis McIntosh, 1885, viz. Polycirrus macintoshi new name. Two species are newly synonymised: Polycirrus insignis Gravier, 1907 (senior synonym P. antarcticus (Willey, 1902)) and Polycirrus habitats Carrerette & Nogueira, 2013 (senior synonym, P. clavatus (Kinberg, 1867)). In addition, several previously synonymised species are reinstated. All available names in the genus are tabulated with type species and type localities and their taxonomic status is assessed. A key to all valid species is provided.