EN
Some adaptations to endoparasitism in 20 species and 2 subspecies of euglenoid parasitic flagellates ihabiting gut of fresh water Copepoda have been studied. The trophozoites, dividing and flagellate forms have been examined by means of morphometric, morphological and cytochemical methods at light and electron microscope level. The developmental cycle, specificity and ecological conditions were analysed for establishing adaptative features. Three groups of species can be distinguished according to degree of their adaptations into parasitic way of life.