The karyotype of Trichobilharzia regenti Horák, Kolárová et Dvorák, 1998 (Digenea: Schistosomatidae), a nasal avian schistome in Central Europe.

The karyotype of a European bird nasal schistosome, Trichobilharzia regenti Horák, Kolárová et Dvofák, 1998, was determined. The chromosome set comprises eight pairs, seven of which are autosomes and one sex pair consisting of ZZ in males and ZW in females. The Z is the largest chromosome of the set, having a submeta-metacentric location of centromere, while the W is a small metacentric chromosome. More than 60% of the analyzed cells originating from both male and female sporocysts contained one or two small submetacentric supernumerary B chromosomes, occurring more frequently in female than in male cells. The formula of the karyotype structure is 2n = 16 + (B), n=5m+1sm-m+ 1sm+Zsm-m/Wm+(Bsm). The C-banding method revealed small pericentric heterochromatin blocks in the sex chromosome Z and all autosomes, except pairs 5 and 6. Satellited pair 5 showed a distinct terminal band representing the nucleolar organizer. Both the W and B chromosomes contained conspicuous heterochromatin blocks at the long arm adjacent to the centromere. The currently described supernumerary chromosomes in T. regenti represent the first record of B chromosomes within the family Schistosomatidae.