AbstractA new species of the genus Pacificabathynella Schminke and Noodt, 1988 is described from groundwaters of Alaska (USA). This is the first record of Bathynellacea Chappuis, 1915 from the far north of America. Pacificabathynella has hitherto been known only from the states of California (one species) and Montana (three species). Pacificabathynella and Paradoxibathynella Serban, 2000 are the only genera that show sexual dimorphism in thoracopod VI. Pacificabathynella yupik sp. nov. has several unique features within the genus: antenna eight-segmented; antennule only slightly longer than the antenna; the setal formula of the maxilla (7/3/7/5); without seta on the endopod of the male thoracopod VIII; five spines on the endopod of the uropod and the endopod as long as the sympod. The new species further shows slight differences in the antennula, pars molaris of the mandible, in thoracopod I–VII and in thoracopod VIII of males and females with the other species of the genus. Sequences of mitochondrial DNA...