Karyological studies on oculate and fin-tailed cercariae from Melanopsis praemorsa collected in Israel

Karyological studies were conducted on three oculate cercariae - Cercaria levantina 18 (number of chromosomes, 2n=12), and Cercariae melanopsi VI and VII (number of chromosomes, 2n=14). The cercariae were obtained from naturally infected Melanopsis praemorsa snails collected in northern Israel. The sizes and morphology of the chromosomes were determined. It was shown that Cercaria levantina 18 and C. melanopsi VI and VII have two distinct groups of chromosomes, one comprising large-sized and the other smaller chromosomes. In both, the size-ratio between the 2 groups was 1.5:1. The 2 C. melanopsi cercariae displayed indistinguishable karyotypes. The main difference between the karyotypes of C. levantina 18 and the two C. melanopsi lay in the number and morphology of their small-sized chromosomes. Basing of the similarity of the genome structure of the studied cercariae we accept that all three cercariae seem to belong to the same genus of trematode. The morphometric characteristics of the chromosomes of these 3 cercariae closely resembled those of a variety of opisthorchioid trematode species described in the literature, and they probably belong to that group of trematodes.