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. Spines hollow , 0.15 µm in diameter near the base and tapering to about 0.10 f.Lm distally . Tip of spines 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, 1.0-204 x 1.3-3.6 µm. Perifery of 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.