Acanthocystis clavata Dürrschmidt, 1987
Diagnosis: Periplast, 25-30 µm, in diameter (measurement based on whole mount); details of protoplast unknown. There are two types of scales: plate scales and nail-like spine scales. Plate scales, 1.3 X 0.77 µm, are elliptical and slightly curved or ovoid. They are thin and patternless, except for a poorly developed central thickening. Spine scales, up to 10 µm long, straight or moderately curved, with a circular baseplate, 0.4 µm in diameter. Shaft presumably solid, slightly narrowing to a thin, but blunt apex.
Ecology: Freshwater, from Banado Cruces, Chili.
Remarks: There is a certain similarity between A. clavata and A. spinifera Greeff (1869) as regards size and shape of cells and spine scales. Investigations by Nicholls (1983) and Dürrschmidt (1985) have revealed that there are several species of almost identical light microscopic appearance, which is why an identification of A. clavata with A. spinifera appears rather arbitrary. With an electron microscope A. clavata can be easily recognized by the shape of the spine scales. It is distinguished from all other so far known Acanthocystis species by its tapering shaft and closed apex.