A chromosome study in the progenetic cestode Cyathocephalus truncatus (Cestoda:Spathebothriidea).

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 polypoid cells (34.7%) was noted in preparations. The chromosomes are comparatively large, up to 12.26 microns. According to centromeric index values, chromosomes 1 and 4 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.