Karyological studies on three strigeid digeneans: Ichthyocotylurus erraticus (Rudolphi, 1809), I-variegatus (Creplin, 1825) and Apatemon gracilis (Rudolphi, 1819)

Previous work has shown that karyology may be a valuable technique for disc riminating morphologically similar species. In the present study, chromosom e number and morphology were described for three strigeid species, Ichthyoc otylurus erraticus (Rudolphi, 1809), I. variegatus (Creplin, 1825) and Apat emon gracilis (Rudolphi, 1819). The results show that these species possess the same diploid number of chromosomes (2n = 20) in somatic cells. The rel ative length and the position of the centromere were determined, and signif icant interspecific differences in the karyotypes are demonstrated, enablin g the ready discrimination of I. erraticus and I. variegatus cercariae. A r eview of known karyotypes of the family Strigeidae suggests that possible r outes of evolutionary changes involve pericentric inversions within chromos omes rather than Robertsonian translocations between elements.