Pelomyxa

Pelomyxa is a genus of giant flagellar amoeboid protists, usually 500-800 μm but occasionally up to 5 mm in length, found in anaerobic or microaerobic bottom sediments of stagnant freshwater ponds or slow-moving streams.

The genus was created by R. Greeff, in 1874, with Pelomyxa palustris as its type species. In the decades following the erection of Pelomyxa, researchers assigned numerous new species to it. However, in the last quarter of the 20th century, investigators reduced the genus to a single species, Pelomyxa palustris, which was understood to be a highly changeable organism with a complex life cycle, whose various phases had been mistaken for separate species. All described species were relegated to the status of synonyms, or moved to the unrelated genus Chaos.