| Summary: | Two specimens from the Koko Seamount (Koko Guyot), in the Hawaiian-Emperor seamount chain, Central North Pacific, caught in 2009 and 2010 are here described as a new species, <i>Bidenichthys okamotoi</i>. The taxonomy of the species in the genera <i>Bidenichthys</i> Barnard, 1934, and <i>Fiordichthys</i> Paulin, 1995, has been confusing due to the lost type of <i>B. consorbrinus</i> (Hutton, 1876) and the rarity of some of the species. Following the synonymization of <i>Fiordichthys</i> Paulin, 1995, with <i>Bidenichthys</i> by Møller and Nielsen 2015 and of <i>Bidenichthys beeblebroxi</i> Paulin, 1995, with <i>Bidenichthys consobrinus</i> Hutton, 1876, the genus <i>Bidenichthys</i> now comprises five species: <i>B. capensis</i>, <i>B. consobrinus</i>, <i>B. okamotoi</i>, <i>B. paxtoni</i> and <i>B. slartibartfasti</i>. <i>Bidenichthys okamotoi</i> differs from its congeners in, e.g., the fewer precaudal vertebrae (12 vs. 13), more palatine teeth rows (4–6 vs. 2–3), shorter pelvic fins (12.1–13.4% vs. 14.4–21.0% SL), max size (187 vs. 147 mm SL) and the shape of the sulcus of the otolith. We here present an updated diagnosis of the genus. A computed tomography (CT) scan of the holotype of <i>B. okamotoi</i> provides for additional anatomical details. The disjunctive occurrence of <i>Bidenichthys okamotoi</i> on the Emperor Seamount chain about 7500 km from the nearest congeneric taxon in New Zealand is discussed. The fossil otolith-based record of the genus <i>Bidenichthys</i> and its systematic implications is briefly discussed.
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