The Japanese mystery snail Bellamya japonica is closely related and biologically similar to B. chinensis. To date, there is debate regarding whether these two taxa should be treated as separate species or simply different phenotypes of the same species, however, Smith (2000) showed clear and consistent differences in shell morphology and anatomy between the two taxa, particularly with respect to the embryonic shell. Consequently recent literature has considered them different species (e.g., Mills et al., 1993; Smith, 2000; Soes et al., 2011; Kipp & Benson, 2011).
Both B. chinesis and B. japonica grow allometrically (the height increasing faster than the width), but B. japonica does so at a faster rate than B. chinensis, so that the adult shell is more elongate than its congener (Jokinen, 1982). The radula also may also differ between B. japonica and B. chinensis, but the considerable variation even within one species suggests that this is not a good diagnostic characteristic (Smith, 2000). However, as a general guide, in one North American population, the radula of B. chinensis had seven small cusps on the marginal tooth and a large central cusp with four small cusps on either side (Jokinen, 1982).