The nature and features of organization of reserve polysaccharides in three species of the genus Pelomyxa-P. palustris, P. belevskii, and P. stagnalis-were studied using light and transmission electron microscopy. We applied the periodic acid-Schiff reaction that is a highly selective method for detecting glycogen. The fluorescent dye auramine-SO2 (Au-SO2) was used as a Schiff-type reagent. The densely packed aggregates of glycogen that form the morphologically differentiated organelle-like bodies are revealed in the cytoplasm in all studied species. The organization of these bodies is characterized by the species-specific features, while in most cases, their size and number in the cells vary depending on the season of the year. Although in all the cases we studied, these bodies do not have their own boundary membrane, in fact, they are surrounded by membranous structures. These structures differ in a variety of Pelomyxa species. We concluded that there are two groups of species in the genus Pelomyxa. The first one includes organisms containing glycogen structures in the cytoplasm (P. palustris, P. belevskii, P. stagnalis, P. binucleata, P. corona, P. secunda). No inclusions resembling glycogen bodies were found in P. flava, P. paradoxa, P. gruberi, and P. prima that form the second group.
Keywords: Electron microscopy; Fluorescent microscopy; Glycogen bodies; Light microscopy; Pelomyxa.