Species of Antarctoscyphus Peña Cantero, García Carrascosa and Vervoort, 1997 (Cnidaria: Hydrozoa: Symplectoscyphidae) collected by US Antarctic expeditions: biogeographic implications

Antarctoscyphus is one of the most characteristic genera of Antarctic benthic hydroids, with nine of the 10 known species considered to be endemic to the Antarctic; only Antarctoscyphus elongatus is also present in the sub-Antarctic region of Kerguelen. Accordingly, the genus was considered to have an Antarctic–Kerguelen distribution. Here we present the results of the study of the species of Antarctoscyphus collected from different Antarctic areas and from the Magellan region, during several expeditions under the United States Antarctic Research Program between 1958 and 1986. A scanning electron microscopy survey of all known species of the genus was carried out. Eight of the 10 known species of Antarctoscyphus were found in the collection, with A. spiralis and A. elongatus being the most frequently found species, whereas A. biformis , A. fragilis and A. gruzovi were found only once. The type material of A. biformis was reviewed and re-described. This study represents the second records for A. biformis and A. fragilis . The new records allow updating of the biogeographic knowledge on the distribution of several species: A. mawsoni , so far considered endemic to East Antarctica, and A. asymmetricus , considered endemic to West Antarctica, are here considered to have a Circum-Antarctic distribution. Additionally, A. fragilis , previously considered endemic to the Weddell Sea, is now considered to have a West Antarctic–Patagonian distribution, as it was recorded off the Pacific Magellan region. The records gathered here allow us to change the distribution pattern of the genus from Antarctic–Kerguelen to Pan-Antarctic. The study has allowed us to increase the known bathymetric range for some species, some reaching much deeper waters than previously known. Hence, A. fragilis , A. grandis and A. mawsoni , hitherto considered shelf species, are reported from bathyal bottoms of the continental slope. A general discussion on the bathymetric and geographic distribution of all known species is included. www.zoobank.org/urn:lsid:zoobank.org:pub:1C7ED3F2-3FF1-4C5C-85BB-FAAF557AC2ED