Atlantapseudes tridens sp. nov. (Tanaidacea: Apseudidae) from the Okinawa Trough, Japan, with a note on the taxonomic status of Atlantapseudes curvatus

The deep-sea apseudid genus Atlantapseudes Băcescu, 1978 currently contains six described species. The distinction between the type species (A. nigrichela Băcescu, 1978) and A. curvatus Esquete & Cunha, 2017 is problematic, because it is unclear whether the holotype for A. nigrichela has a tridentate or monodentate rostrum. We observed and redescribed the type material of A. nigrichela and concluded that A. nigrichela and A. curvatus are conspecific, i.e., the latter is a junior synonym of the former. Additionally, we amended the diagnosis of A. nigrichela and treated the form of A. nigrichela with a monodentate rostrum in Băcescu (1978) as an unidentified species. We also found that Atlantapseudes sp. sensu Kakui et al. (2011), the first record of this genus from the North Pacific, was undescribed; here we describe it as Atlantapseudes tridens sp. nov. The new species resembles A. nigrichela in having a tridentate rostrum but differs in having (1) pereonites 1–3 without posterolateral spines; (2) a tiny anterolateral spine on pereonite-6; (3) two distal bifurcate spiniform setae on the labial palp; and (4) one outer distal seta on maxillipedal palp article-2. We present a partial nucleotide sequence for the cytochrome c oxidase subunit I (COI) gene from A. tridens sp. nov. for future DNA barcoding.