Genus Pelomyxa Greeff, 1874
Diagnosis: Free-living amoebae from anaerobic or micro-aerophilic habitats, cells amoeboid, reaching 5 mm long with a large anterior pseudopod and a posterior uroid; shell usually spherical to elongated ovoid; one to numerous nuclei; short flagella present in most species; cytoplasm filled contains several glycogen bodies; different types of symbiotic bacteria have been observed; all pelobionts lack mitochondria.
Remarks: Pelobionts are an original group of amoeboid protists inhabiting bottom sediments of freshwater basins under micro aerobic or anaerobic conditions. Earlier investigators described nearly twenty species. Later, the validity of most species was doubted and studies of Chapman-Andresen, (1978, 1982) showed a complex life cycle, and all Pelomyxa species ever described, were considered to be stages of the life cycle of Pelomyxa palustris. This led to the conclusion that Pelomyxa palustris was a polymorphic species.
Since 2004, a series of studies by Frolov et al (2004, 2005, 2006, 2011) changed this view completely. They provided evidence that some original described species are valid species an no part of a complex life cycle of Pelomyxa palustris. Concerning the latter, it is still unclear whether P. palustris is a nominal species or a group of species erroneously united into a single taxon.
Pelomyxa representatives are multinuclear and possess numerous immobile flagella. All pelobionts lack mitochondria and most, with the exception of Mastigamoeba punctachora and P. palustris, the Golgi apparatus.
Key to Pelomyxa species:
|1||Usually with two nuclei||2|
|–||Usually with more than two nuclei||3|
|2||Nuclei < 30 µm||P. flava|
|–||Nuclei > 30 µm||P. binucleata|
|3||Cell with numerous conical projections||P. corona|
|–||Cell without such projections||4|
|4||Nucleus with central nucleolus||5|
|–||Nucleus with small peripheral nucleoli||P. palustris|
|5||No glycogen bodies present||P. gruberi|
|–||Glycogen bodies present||P. stagnalis|