PARADIPLOZOON HOMOION (MONOGENEA) DIGESTIVE TRACT ON THE FINESTRUCTURE LEVEL
Diplozoons (Monogenea) are blood feeding ectoparasites of fish with specific cross body arrangement of two permanently fused adult individuals. Each has two large bucal suckers and a muscular pharynx in the anterior part and an opisthaptor with scleroprotein clamps and hooks in the posterior part of body. Whereas these conspicuous morphological structures have been frequently studied, details of internal morphology and ultrastructure are little known. Specimens of P. homoion were obtained from the gills of common bleak Alburnus alburnus; the fish were caught in the littoral zone of Musov lowland reservoir (South Moravia, Czech Republic) The fish gills were checked using stereo microscope for the presence of all diplozoid ontogenetic stages. Founded parasites were fixed by 2% osmium tetroxide, dehydrated through ascending acetone series and immediately embedded in a Spurr resin. All sections were obtained by Leica EM UC6i ultramicrotome. Semi thin sections were stained by toluidine blue and ultra thin sections were contrasted by uranyl acetate lead citrate. Ultra thin sections were examined by transmission electron microscope operating at 60 kV (JEOL JEM 1010) equipped with Megaview II software. In this study, the ultrastructural details of the gastrointestinal tract of this worm which represent a unique documentation of specialised structures such as buccal suckers, pharynx with pharyngeal glandular cells, haematin cells and the ultrastructural view of the gut lumen with intact erythrocytes, were documented. Our findings support the hypothesis that the mechanism of P. homoion digestion is predominantly intracellular.