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. Since 2004,
four new Pelomyxa species have been described, and two older
species have been redescribed and confirmed as valid members of
the genus. These developments have raised new questions about
the nature of Pelomyxa palustris itself. Pel