Naegleria gruberi (Schardinger, 1899) Wilson, 1916

Diagnosis: Cysts spherical to ovoid, usually smooth-walled, but with thin outer wall separated in some (rough) strains which often have a more irregular over-all form; several pores containing plugs discernible with light microscope (prominent in rough strains); usually a perinuclear layer of coarse granules in cysts, often in amoebae; most strains transforming readily to flagellates between 20°C and 25°C.

Dimensions: cysts 9-23 µm, mean 10-16 µm (according to strain, Page); my measurements: amoeboid form c. 21-24 µm, nucleus 3.5-3.7 µm, cysts 8.3-13.4 µm.

Ecology: common in freshwater and terrestrial habitats. Possibly the most common freshwater amoeba and apparently world-wide in occurrence.