Pelomyxa stagnalis  Chystyakova and Frolov, 2011


Diagnosis: Large multinucleate pelomyxa with lengths that can exceed 800 µm. The cell shape is oval or pear-shaped and the uroid, if present, has a bublike shape. During movement, the cytoplasm flows are uniform and the fountaining cytoplasm movement at the anterior end of the cell is not pronounced. The predominant staining of the cytoplasm is greenish brown. The number of nuclei in the cell is 30–50. Nuclei are rounded, their size is 25–30 µm, and they are often surrounded by a brush border composed of optically dense granules. The nucleolus is central and usually solid and rounded, sometimes composed of two to three irregularly shaped lobes. In the cytoplasm, two species of the rodlike bacterial endobionts are present. The flagellar basal body is connected with 15–20 microtubules loosely configured at a small angle to the cell surface.


Dimensions: Length up to 800 µm or more. Nuclei 25-30 µm


Ecology: Pelomyxa stagnalis inhabits silts of the coastal zone of stagnant and low-flow freshwater reservoirs and sphagnum swamps; usually it feeds on small particles of detritus, mainly of plant origin, and mineral inclusions are sometimes found in the cytoplasm.


Remarks: P. stagnalis clearly differs from P. palustris, P. corona, P. binucleata, P. prima and P. gruberi by organization and number of its nuclei.