The karyotype of Trichobilharzia regenti Horak, Kolarova et Dvorak, 1998 (Digenea : Schistosomatidae), a nasal avian schistome in Central Europe

The karyotype of a European bird nasal schistosome, Trichobilharzia regenti Horak, Kolarova et Dvorak, 1998, was determined. The chromosome set compri ses eight pairs, seven of which are autosomes and one sex pair consisting o f 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 sma ll metacentric chromosome. More than 60% of the analyzed cells originating from both male and female sporocysts contained one or two small submetacent ric supernumerary B chromosomes, occurring more frequently in female than i n 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 pe ricentric heterochromatin blocks in the sex chromosome Z and all autosomes, except pairs 5 and 6. Satellited pair 5 showed a distinct terminal band re presenting the nucleolar organizer. Both the W and B chromosomes contained conspicuous heterochromatin blocks at the long arm adjacent to the centrome re. The currently described supernumerary chromosomes in T. regenti represe nt the first record of B chromosomes within the family Schistosomatidae.