Pycnogonida (Arthropoda) from Uruguayan waters (Southwest Atlantic): annotated checklist and biogeographic considerations

Records of pycnogonids from Uruguayan waters (south-western Atlantic) include 26 species cited from precise locations, and at least five other species based on unconfirmed records. Nearly half of the species in that fauna belong to the genus Nymphon (12 spp.). Most species (22) come from deep-water and were recorded and described by C. A. Child. Of these, at least twelve species have an extended Antarctic and Subantarctic distribution, showing the influence of these cold waters in the area; three others have a wide deep-sea distribution pattern. Five species are known only from the lower slope and abyssal basin off La plata river: Mimipallene Atlantis and four species of Nymphon. Records from coastal and shelf areas (four species) are poorly documented and should be the focus of future research. Of these, Colossendeis geoffroyi is considered endemic in the Southwest Atlantic between 34 degrees S and 40 degrees S, but presents clear Antarctic affinities. A small-sized species living in shallow waters, Pycnogonum cessaci, is here considered as cryptogenic.