A new antarcturid isopod, Oxyarcturus holoacanthus sp. nov., is fully described based on seven specimens collected in the Mar del Plata submarine canyon at 2950 m depth, during the “Talud Continental III” expedition on board the Argentinian RV “Puerto Deseado”. Oxyarcturus holoacanthus sp. nov. is closely related to O. spinosus (Beddard, 1886), from which it can be distinguished by the body spine pattern. The penial plate, a novel character for the genus Oxyarcturus, as well as for the family Antarcturidae, is described in detail. The species O. dubius (Kussakin, 1967) and O. beliaevi (Kussakin, 1967) are considered as incertae sedis until further morphological and molecular data can clarify their taxonomic position. An update of the geographic and bathymetric records of the genus Oxyarcturus is provided.