Exotic freshwater planarians currently known from Japan

Biogeographical and taxonomic information on the four non-indigenous freshwater planarians of Japan is reviewed, viz. Dugesia austroasiatica Kawakatsu, 1985, Girardia tigrina (Girard, 1850), G. dorotocephala (Woodworth, 1897), and Rhodax evelinae? Marcus, 1947. The occurrence of Girardia dorotocephala in Japan is unequivocally demonstrated. New karyological data are presented for populations of D. austroasiatica (chromosome complement: 2x=16, 3x=24), G. tigrina ( 2x=16, 3x=24), and G. dorotocephala (2x=16). The following factors may have facilitated the introduction and subsequent geographical spread of exotic freshwater triclads in Japan: popularization of domestic tropical fish cultures, and culture of exotic aquatic animals for food.