One of the most commonly encountered genera of freshwater snails in the Far East Asia is
Semisulcospira. More than 18 species and subspecies of this genus have been described from China (
Yen, 1939). Identification of these species is difficult due to the great amount of variation in shell shape, structure and coloration. In the Pleuroceridae, the family to which
Semisulcospira is presently referred about chromosomes, 12 species have been studied from Japan and eight species from Korea (
Patterson, 1967;
Burch, 1968;
Park, 1994).
Semisulcospira libertina (=
bensoni) is regarded as the most important intermediate host of
Paragonimus westermani (
Yokogawa et al., 1960a,
1960b). Several nominal subspecies of
S. libertina have also been implicated as intermediate hosts for paragonimiasis and metagonimiasis in humans and other mammals in the Far East. However, a little is known concerning the biological relationships of the nominal species of
Semisulcospira over its wide range of geographic distribution (China, Formosa, Japan and Korea), and the relationship of
S. libertina to other melaniid snails.
Semisulcospira dolichostoma is a pleuracerid species in mainland China, and no information on the susceptibility of human-infecting trematodes is available. Although some viviparid snails such as
Cipangopaludina spp. act as the second intermediate host of echinostome trematods, the parasitological role of
V. rivularis has not been reported yet. Therefore, further studies on the susceptibility tests of these snails to trematodes are needed. Patterson (
1967) found 18 bivalents in each of the specimens of
S. libertina that were studied from four localities in Japan. Inaba and Tanaka (
1953) reported
S. libertina to have eight pairs of chromosomes (n=8, 2n=16). In this study, however, all specimens of this species had 18 bivalents. Burch (
1968) also found
S. libertina to have a haploid chromo-some number of n=18. We therefore mention that Inaba and Tanaka's report (
1953) of only eight pairs of chromosomes for this species is in error. Burch (
1968) extended our cytological knowledge of
Semisulcospira by studying eight additional species in which the haploid chromosome numbers ranged from n=8 to n=20. With such a wide variation in chromosome numbers, the pleuroceridae has been proven to be a group of considerable cytogenetic interest. Park (
1994) has reported on the chromosomes of eight species of pleuroceridae in Korea. The six species of
Semisulcospira in his study had chromosome number of n=18 and 2n=36. It is obvious that chromosome number is more conserved in species of
Semisulcospira in Korea than those in Japan or China. Park (
1994) reported that the karyotyping is especially helpful for analyzing
Semisulcospira in Korea, since all species studied so far from Korea have the same chromosome number (n=18, 2n=36).
Semisulcospira forticosta and
S. tegulata can be distinguished by their karyotypes.
In the Viviparidae, the chromosome number of all species studied so far is n=7 to n=14 (
Patterson, 1969;
Zhou et al., 1988;
Park et al., 1997). In the most primitive viviparid subfamily, Bellamyinae, the haploid chromosome numbers of 11 species studied range from 8 to 11 (
Ramamoorthy, 1958;
Inaba, 1965;
Zhou et al., 1988). In the subfamily Viviparinae, the haploid number of eight species ranges from n=7 to n=13 (
Rainer, 1963). Recently, Park et al. (
1997) reported the chromosome numbers in two species of echinostome vector snails of the family Viviparidae in Korea. In the present study, however, the chromosome number of
V. rivularis is different from those of the former reports.