A new species of ectosymbiotic branchiobdellidan, Cirrodrilus iwakiensis sp. nov., is described from Cambaroides japonicus (de Haan, 1849), the endemic freshwater Japanese crayfish, collected in Aomori Prefecture, northern Honshu Island, Japan. The anatomical features used to identify C. iwakiensis are compared with those of its closest congener, C. nipponicus (Yamaguchi, 1932), as well as C. aomorensis (Yamaguchi, 1934) and C. tsugarensis Gelder and Ohtaka, 2000 distributed in the same region.