New data on the karyotype and chromosomal rDNA location in Paradiplozoon megan (Monogenea, Diplozoidae), gill parasite of chubs.

New morphological data on chromosome complement of diplozoid parasite Paradiplozoon megan from the chub Squalius cephalus are shown herein. The karyotype of P. megan is characterized by seven pairs (2n = 14) of medium long (up to 11 μm) one-armed chromosomes which are nearly identical in number and morphological classification with chromosomes of other Paradiplozoon species described karyologically to date (Paradiplozoon bliccae, Paradiplozoon nagibinae, Paradiplozoon sapae, Paradiplozoon pavlovskii and Paradiplozoon homoion). A single locus for ribosomal RNA genes, visualized in the secondary constriction site by the fluorescent in situ hybridization method, is situated interstitially on a median part of a long arm of the smallest, 7th chromosome pair in P. megan. Phylogenetic interrelationships within the members of the family Diplozoidae and hypothesis for the ancestral karyotype are discussed here.