The polymerase chain reaction with arbitrary (RAPD-PCR) or specific primers was used to study the population variation and to identify the species in cercariae of schistosomes of the Trichobilharzia ocellata species group (Trematoda, Schistosomatidae). In total, 28 cercariae were obtained from two spontaneously invaded mollusks Lymnaea stagnalis (LS) and L. ovata (LO), which were collected in different ponds of Moscow. RAPD-PCR was carried out with two arbitrary primers, OPA9 and OPB11, which each detected different levels of individual and among-group variation and revealed considerable genetic differentiation of cercariae from different host mollusks. To check whether the cercariae of the two samples belong to one species, sequencing was performed with a region corresponding to intergenic transcribed spacer 2 (ITS2), which was earlier proposed for cercaria identification in three European species of bird schistosomes of the genus Trichobilharzia ( T. franki, T. regenti , and T. szidati ). The ITS2 sequences of two LO cercariae were identical, each consisted of 319 bp, and showed 100% homology to the T. franki ITS2 sequence. The ITS2 sequences of two LS cercariae were identical, each consisted of 323 bp, and showed 99.4% homology to the T. szidati counterpart. The causes of genetic variation in cercariae and prospects of using RAPD markers to study different stages of the life cycle in trematodes are discussed. MOLECULAR GENETICS

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The polymerase chain reaction with arbitrary (RAPD-PCR) or specific primers was used to study the population variation and to identify the species in cercariae of schistosomes of the Trichobilharzia ocellata species group (Trematoda, Schistosomatidae). In total, 28 cercariae were obtained from two spontaneously invaded mollusks Lymnaea stagnalis (LS) and L. ovata (LO), which were collected in different ponds of Moscow. RAPD-PCR was carried out with two arbitrary primers, OPA9 and OPB11, which each detected different levels of individual and among-group variation and revealed considerable genetic differentiation of cercariae from different host mollusks. To check whether the cercariae of the two samples belong to one species, sequencing was performed with a region corresponding to intergenic transcribed spacer 2 (ITS2), which was earlier proposed for cercaria identification in three European species of bird schistosomes of the genus Trichobilharzia ( T. franki, T. regenti , and T. szidati ). The ITS2 sequences of two LO cercariae were identical, each consisted of 319 bp, and showed 100% homology to the T. franki ITS2 sequence. The ITS2 sequences of two LS cercariae were identical, each consisted of 323 bp, and showed 99.4% homology to the T. szidati counterpart. The causes of genetic variation in cercariae and prospects of using RAPD markers to study different stages of the life cycle in trematodes are discussed. MOLECULAR GENETICS