Bathynoe carcadiensis n. sp. is described from trawl collections taken on Cascadia Abyssal Plain in the north-eastern Pacific Ocean off the coasts of Oregon and Washington, U.S.A. Both females and the smaller males are found clinging to the actinostome and ambulacral grooves of the deep-water brissingid asteroids Astrocles actinodetus Fisher, 1917, and Astrolirus panamemis (Ludwig, 1905). One hundred and twenty-three specimens have been examined in detail, and the morphology, biology and distribution of the species are discussed. Variability is noted in the shape of the dorsal cirri and in the shape and attachment sequence of the posterior elytra. In addition to the new species, the genus Bathynoe now encompasses B. tuberculata (Treadwell, 1906), new combination, B. pustulata (Horst, 1915), B. nodulosa Ditlevsen, 1917, and B. pacifica Uschakov, 1950, new combination.