Six species of the fresh water snail were collected from a total of 29 sampling sites. To evaluate genetic variability within and between populations, enzymes coded for by 18 presumed loci were examined by starch gel electrophoresis.
Out of the six species, three (S. niponica, S. multigranosa and S. nakasekoae) were endemic to the Lake Biwa and remaining three (S. libertine, S. reiniana and S. kurodai) were the snail species widely distributed throughout Japan. The proportion of polymorphic loci and the expected average heterozygosity per individual for the three endemic species were 0.120±0.069 and 0.019±0.003, respectively. Those for the three widespread species were 0.179±0.068 and 0.058±0.017 (mean±S.D.), respectively. The present result showed that the S. kurodai, which has been considered to be transitional between the S. libertine and S, niponica complexes (Davis, 1969), should be classified into the Davis′s S. libertina complex.