Scheme summary the distribution of C-banding pattern (represented in left side), 18S rDNA (green) and as well as true telomeres (at the ends) and interstitial telomeric (ITS – in the inner parts) repeats (red) of Gonatoxia helleri. Three chromosome pairs (1st and polymorphic 2nd and 3rd) in main karyomorphs [homozygous metacentric (1A hom, 2A hom, 3 hom), heterozygous – submeta/ acrocentric (2B het, 3 het), homozygous acrocentric (2C hom)] and X chromosome showed differences in the size and position of rDNA and tDNA signals detected by FISH and generally demonstrate a coincidence between the location of rDNA loci and C-positive heterochromatin regions. The presence of ITSs near the pericentromeric and interstitial and/ or near telomeric region suggest that karyomorphs could be the result of different chromosomal rearrangements.