Acanthocystis pusilla (Dürrschmidt, 1987) Siemensma, 1991
Diagnosis: Periplast, 25-35 µm in diameter (measurement based on whole mount), with 2 types of scales. Details of protoplast unknown. Plate-scales 2.7-3.0 X 1.1 to 1.4 µm, pear-shaped or more rarely elliptical with a median constriction. A short axial thickening is present together with numerous dots, arranged in more or less concentric circles. Spine-scales, 3.9-6.6 µm long, consist of a hollow cylindrical shaft (ca. 0.25 µm in diameter) protruding from a circular base-plate (1.0-1.5 µm in diameter). Distal ends with a slight flaring and 4-7 marginal teeth.
Ecology: Freshwater. from a paludal forest near Puerto Varas, southern Chile.
Remarks: A. pusilla is distinguished from genuine A. penardi by the presence of only one type of spine-scale, by the longer and less numerous apical teeth (4-7 as compared to 8-14) and on the basis of considerably smaller cells and scales.