Abstract

The distribution, external morphology, radula, chromosome numbers of Planorbidae snails were studied. The specimens were collected at four stations in Nonsangun, Kongjugun, and Daedukgun which are located around Geum river. Three genera and three species of Planorbidae, Hippeutis cantori, Segmentina hemisphaerula and Gyraulus convexiusculus, were collected. H. cantori was the most abundant species among the three species. G. convexiusculus was the least abundant one. Each species could be identified on the basis of its external characteristic, since the periphery of each species has a peculiar shape. H. cantori was the largest one among the three species. The radula formula of each species was very similar to other species. The size of radula was proportional to the size of shell. The radula formulae of H. cantori, S. hemisphaerula, and G. convexiusculus were 29:1:29, 23:l:23, and 16:1:16 respectively. The difference of radula formula could be found in the total numbers of laternal and marginal teeth. The haploid chromosome number of H. cantori was eighteen (n=18). S. hemisphaerula and G. convexiusculus were assumed to be same in their chromosome numbers (n=18).