Columbasellus acheronc a nw genus and species of subterranean isopod from Washington lCrustaceac Isopodac Asellidaer

Columbasellus acheron, new genus, new species, is described from a male specimen discovered during the cleaning of the municipal water well of Kalama, Washington. The genus Columbasellus is geographically closest to the genera Caecidotea, Calasellus and Salmasellus, but is morphologically more similar to the Eurasian Asellus aquaticuslhilgendorfii complex of species, with which it shares a male pleopod 2 that possesses a relatively large labial spur and basal spur, and fully formed, ovate exopods in pleopods 4 and 5. Columbasellus acheron inhabits the hyporheic zone of the Kalama River. Evidence is presented that indicates widespread use of stream gravel interstices by subterranean isopods in the Pacific Northwest, including the first record of Salmasellus howarthi from Oregon.