Distribution of heterochromatin after DAPI-staining (blue; ZŠ population) (A–B), two-color FISH with 18S rDNA (green) and H3 histone (red) probes on chromosomes of Acanthocephalus anguillae males from the ZŠ population (C–F) and FISH with H3 histone probe (red) on chromosomes of A. anguillae males from the HN population (G–I). A Mitotic metaphase with B chromosome and B two anaphase nuclei, left with and right without B chromosome. C Mitotic metaphase. D Two pachytene nuclei, the left with nucleolus residue (N). E Diplotene. F Pachytene with B chromosome. G Mitotic metaphase. H Pachytene. I Diplotene. Arrows indicate the B chromosome and asterisks indicate the X chromosome. Bar = 10 μm.