Acanthocystis valdiviense   Dürrschmidt, 1987

Diagnosis: Periplast, 20-25  µm in diameter (measurement based on whole mount), with 3 kinds of scales. Details of protoplast unknown. Plate-scales, 1.2-1.8×1.0 to 1.5 µm, elliptical or ovoid, periphery with a small thickened rim, and with an axial thickening poorly developed and sometimes asymmetrically placed in the centre. Otherwise they are thin and patternless. Spine-scales of two kinds, all with tubular straight shafts (0.17  µm in diameter), round base-plates (0.58 µm in diameter) and apically always with 4 pointed teeth. The base-plates are centrally depressed and surrounded by a narrow marginal rim. One kind of the spine scale (S1) is 5-7 µm long, with only slightly expanded distal ends and short distal teeth. The other (S2) is usuall half as long (ca. 2.6 µm) with distinctly expanded apices and longer apical teeth.

Ecology: Freshwater. Collected in 1979 from a paludal forest in southern Chile.

Remarks: The most distinctive characteristics of A. valdiviense are (1) the fixation of the number of apical points to 4 (6-8 in A. pectinata sspp. and A. polymorpha), (2) the minor flaring of the distal portion of spine scale type (S2) (0.4-0.6 µm compared to 1.1-1.5  µm in A. pectinata sspp. and ca. 2.0 µm in A. polymorpha), and (3) the length of the cylindrical portion of the shaft (2.2 µm compared to 1.3 µm in A. pectinata and 4-8  µm in A. polymorpha). There are also differences in the appearance of the plate-scales. These are conspiciously larger in the case of A. polymorpha and more electron dense, while in A. pectinata sspp. additional ornamentations such as slits and dots are developed.
A. valdiviense bears also a certain resemblance to A. pusilla, for instance in the shape of the spine-scales. However, both taxa are distinguished by the presence of only one type of spine scale, by the varying number of apical teeth (4-7), the less expanded distal ends, and by the pyriform and dotted plate-scales.