Choanocystis cordiformis  (Dürrschmidt, 1987) Siemensma, 1991
Syn.: Acanthocystis cordiformis Dürrschmidt, 1987
  

Diagnosis: Periplast, 40-50 µm in diameter (measurement based on whole mount), with two types of scales; details of protoplast unknown. Spine scales (11), 16-20 µm long, narrow, consisting of shaft and base-plate. Shaft, 0.15-0.25 µm in diameter, cylindrical, solid (?), tapering slightly to a blunt apex with 4-6 tiny marginal teeth. Proximal part of the shaft sometimes with minute siliceous nodules. Base of the spine seated eccentrically on a thin, heart-shaped base-plate, 0.5 µm in diameter. Plate scales elliptical, 1.5-2.2 x 1.0-1.5 µm, patternless, except for an axial thickening.

Distribution: Chile, New Zealand, Sri Lanka.