Abstract
The karyotype of a caryophyllidean tapeworm Caryophyllaeus laticeps (Pallas, 1781) from the freshwater bream Abramis brama (L.) caught in the Slovak part of the River Tisa, was described and originally inspected for amount of heterochromatin and its chromosome localization. The chromosome set comprised nine metacentric and one submetacentric (No. 3) pairs (2n = 20). The chromosomes were up to 12.0 ± 2.5 μm long and the mean total length of haploid genome (TLC) reached 80.6 μm that represents one of the highest yet recorded values among tapeworms. C-banding and staining with fl uorescent dyes DAPI and YOYO1 revealed a distinct banding pattern explicitly on chromosomes with centromeric bright heterochromatin bands present on all 10 chromosome pairs; no pair showed any interstitial heterochromatin. A complete course of spermatocyte meiosis and dynamics of nucleolus formation and degradation during meiotic division was described.