[Light and electron microscopic investigation of Pelomyxa prima (Gruber, 1884) (Peloflagellatea, Pelobiontida)].

Cell organization of a multinuclear pelobiont Pelomyxa prima has been studied at the light and electron microscopic levels. Motile individuals demonstrate a characteristic drop-like or pyriform shape and reach 550 microkm in length. The cell cover is represented by a well-developed, morphologically differentiated glycocalyx 80-100 nm thick. The cytoplasm contains many structural vacuoles. The nuclei are of vertical type, numbering up to several nuclei in large individuals. Numerous cytoplasmic microtubules are associated with the external membrane of the nuclear envelope. Separate non-motile flagella are distributed throughout the cell surface, being more numerous in the posterior body end and uroidal zone of the protist. Basal bodies of the flagella are extremely long, being deeply immersed into the cytoplasm. These bodies are surrounded by a muff of electron-dense material, with numerous microtubules radiating from it. A compact bundle of microtubules starts from the base of a basal body axially into the cytoplasm. Besides, a band-like lateral microtubular rootlet is present. The number of microtubules in the axoneme of undulipodia is unstable. Neither mitochondria, nor Golgi complex were found. Two species of bacterial endocytobionts are present in the cytoplasm in considerable numbers.