Summary: | The chromosomes of somatic cells of progenetic Cyathocephalus truncatus, parasite of amphipod crustaceans, Gammarus lacustris, from North-West Chukotka were investigated using standard Giemsa staining. The karyotype, not described previously, consists of 9 pairs of chromosomes (2n=18), the most widespread number among cestodes. A considerable number of polyploid cells (34.7%) was noted in preparations. The chromosomes are comparatively large, up to 12.26 mu m. According to centromeric index values, chromosomes 1 and 4 are subtelocentric; 2, acrocentric to subtelocentric; 3 and 5, acrocentric; 6 and 9, metacentric; 7, submeta-subtelocentric; and 8, submetacentric. These characteristics are discussed with reference to the karyotypes previously described within other closely related groups caryophyllideans and pseudophyllideans.
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