Quadrulella constricta  Lopretto & Vucetich, 1997

Diagnosis: Shell yellowish, elongated, compressed, with a rounded fundus. Neck separated from the main body by a clear constriction, giving the test a bicameral impression. Neck length corresponding to ca. 1/3rd of the entire test length. Pseudostome curved, with a well-developed organic lip followed by ≥ 1 line of rectangular plates arranged parallel to the lip edge. From this point, plates (size 1.8–2 μm) arranged in a helix, reaching the fundus of the test. Plates generally juxtaposed with little overlap, except for the constriction at the base of the neck.

Dimensions: According to Lopretto & Vucetich (1997): Shell length 168—192 µm; width 83—104 µm; thickness 48—50 µm; aperture 33—48 µm.

Ecology: Among aquatic mosses.

Geographical distribution: Argentina.