Both sexes of a new genus and species of Ancorabolidae are described from the San Diego Trough in the Northeastern Pacific. Arthuricornua anendopodia, new genus, new species, is placed in the newly defined Ceratonotus-group which includes the genera Ceratonotus Sars, Dorsiceratus Drzycimski, and Polyascophorus George. Members of this group are characterized by the cylindrical body shape, presence of dorsal processes on somites bearing P2–P4, rostral shape, proximal antennulary elongation, 3-segmented condition of ♂ P3 endopod, and absorption of P5 endopodal lobe in both sexes. The major evolutionary transformations within the Ceratonotus-group are discussed and polarized by outgroup comparison with the Cletodidae. Parsimony analysis confirmed Dorsiceratus and Ceratonotus as monophyletic genera, but demonstrated the polyphyletic status of Polyascophorus. Polyascophorus schminkei George is identified as the earliest offshoot within the Ceratonotus-group and is transferred to a new genus Touphapleura. The common ancestry of Arthuricornua and Dorsiceratus, and the sistergroup relationship between Ceratonotus and Polyascophorus, are strongly supported. A basal dichotomy divides the genus Ceratonotus into two geographically separated clades. The genus Polyascophorus is redefined to include only P. martinezi George and P. gorbunovi (Smirnov).