Thecamoeba foliovenanda Mesentsev et al., 2020

Diagnosis: Oblong amoebae with an extended anterior area and a tapered posterior end. No differentiated uroidal structure is present; the posterior part of the cell is often elevated above the substratum. The single nucleus is spherical or oblong and contains a peripheral monolayer of nucleoli. The nucleolar material consists of individual pieces with flattened, ovoid, or irregular shapes, often containing lacunae.

Dimensions: According to Mesentsev et al. (2020): Length in locomotion 34.1—90.3 µm; width 31.4—83.2 µm; length/breadth ratio 0.8–2.1; nucleus 11.6—19.2 µm; nucleolus 0.4—4.9 µm; thickness of the nucleolus about 1.3 µm.

Geographical distribution: Currently known only from Russia.

Remarks. This new species resembles Thecamoeba similis (Greeff, 1891) sensu Page (1977) but differs in the fine details of nuclear structure and size and (presumably) in glycocalyx structure. It also shows significant differences in the 18S rRNA gene sequence compared to T. similis and other Thecamoeba species, particularly in positions 123–168, 775–848 bp (E23 variable region), 1745–1838, and 2021–2110 bp. All positions correspond to the sequence of the Ta72 strain (MN544293).