Genus Thecamoeba Fromentel, 1874

Diagnosis: Locomotive form, usually between 30 and 350 µm long, flattened and oblong in outline, often with several parallel folds or wrinkles. Anterior edge semi-circular with an extensive hyaloplasm that can occupy more than half the cell. Posterior edge often slightly convex, sometimes with a knob uroid. Form of the nucleus is an important diagnostic feature for delineating species, and thecamoebae can have a single spherical or ovoidal nucleus with a central nucleolus, granular nucleolus, or nucleolus as 2 or 3 parietal pieces. Cytoplasm may have crystals and contractile vacuoles. No cysts known.
At the ultrastructural level, nuclear envelope without an internal fibrous lamina and cell coat as a thick, dense, amorphous, glycocalyx.
Type species. Thecamoeba quadripartita Fromentel, 1874

Habitat: Reported from freshwater, terrestrial, and marine habitats. Common genus with 18 described species.

Remarks: Thecamoeba species cannot be identified based on their light-microscopic characters, such as shape and size of the locomotive form, the presence and typical position of ridges and folds and the structure and the size of the nucleus There are species, which can hardly be distinguished by light-microscopic morphology, or cannot be distinguished, e.g., T. aesculea is almost indistinguishable from T. sphaeronucleolus. Identification of Thecamoeba species based solely on light microscopic data should be taken with great care (Mesentsev, Kamyshatskaya and A. Smirnov, 2020).