Amoeba proteus (Pallas, 1766) Leidy, 1878
Diagnosis: Locomotive cells, often 220 to 760 µm in length; usually polypodial with one dominant pseudopodium, usually with dorsal and lateral folds or ridges; resting or well fed, cells irregularly rounded; floating forms wit h long radiating pseudopodia; cytoplasm granular in appearance, often with truncated bipyramidal or plate-shaped crystals; posterior uroid morulate; nucleus discoid or ovoid, sometimes with peripheral granules; nucleolar material often scattered.
Dimensions: 220-760 µm (mean 425 µm); nucleus 22-62 µm (mean 38-47 µm), discoid, often biconcave.
Ecology: freshwater and wet Sphagnum, in different types of water. Not rare.
Remarks: Though this amoeba has been described as uninucleate, I have often seen multinucleate specimens. In one sample there were amoebae with one nucleus and specimens with several nuclei (see the graph below.)