Light and electron microscopic study of Pelomyxa binucleata (Gruber, 1884) (Peloflagellatea, Pelobiontida)

Summary Morphology of a pelobiont Pelomyxa binucleata (Gruber, 1884) has been studied using light and electron microscopy. The organisation of P. binucleata has been shown to differ from that of P. palustris, P. prima and P. corona. The cell surface of P. binucleata is represented by the plasma membrane with a thin but distinct layer of nonstructured glycocalyx. The ectoplasm, containing a network of fine fibrils, is separated from the endoplasm with a boundary layer of cisterns and reticulum channels. The flagella are poorly motile. The axoneme has a nonstable set of microtubules. A short kinetosome is about 200 nm long; the transition zone, also about 200 nm long, is situated above the cell border and contains a transition cylinder. Microtubular rootlet and microtubular cone are absent. From the kinetosome, almost in parallel to its longitudinal axis, 35�40 microtubules arranged in 3�4 rows start. Right below the kinetosome base they bend at a right angle to its longitudinal axis and pass further as a bundle in the ectoplasm below the cell surface. These microtubules do not penetrate into the endoplasm. The system of structural vacuoles is poorly developed. Glycogen bodies are rounded, smooth and surrounded with flattened reticulum cisterns. The set of endocytobionts includes two kinds of rodlike bacteria: thick bacteria with a poorly developed cleft and thin Grampositive ones. The length of both kinds of bacteria may be 30 µm and more. The nuclear envelope bears a multilaminar layer on its outer surface. The nucleolus is fragmented and situated at the centre of the nucleus. The species composition of the genus Pelomyxa Greeff, 1874 is discussed in the context of revision of outdated ideas about its monotypy. Morphology of its representatives is considered in comparative aspect.