Acanthocystis trifurca  Nicholls, 1983

Diagnosis: Cells (6-) 8-12 (- 18) µm in diameter with scales of two kinds . Spine-scales 2.5-10 µm long and mostly straight or with some curvature near the base. Spine-scales hollow, 0.15 µm in diameter near the base and tapering to about 0.10 µm distally. Tip of spine-scales separated into three arms, 0.08-0.25 µm long, each usually tapered to a sharp point, but sometimes slightly bifurcate or swollen and rounded. Base of spine, a shallow inverted cup, 0.5-0.7 µm in diameter, usually with a thickened marginal rim. Plate-scales circular to elliptical, 1.0-2.4 x 1.3-3.6 µm. Periphery of the plate-scales with a thickened rim, 0.015- 0.030 µm wide. An axial fold or thickening is present in the middle of the scale and occupies up to two-thirds of the length of some scales but is much less developed or absent in others.

Geographical distribution: Freshwater: in lakes and streams. Canada (Nicholls, 1983), Chile (Dürrschmidt, 1985), Netherlands (2018, Siemensma).