Acanthocystis dürrschmidtidae  Wujek, 2003

Diagnosis: Cells 35-40 µm (based on a whole mount). Periplast comprising scales of two types, plate- and spine-scales. Protoplast unknown. Plate-scales are elliptical to broadly ovate, ca. 4-4.5 x 2-2.5 µm, with a narrow rim. Ornamentation consists of an axial thickening surrounded by a distinct pattern of radial slits, each ca. 0.25 µm long and up to 0.03 µm wide, located adjacent to the axial thickening. Small granules are scattered all over the surface, sometimes regularly arranged in radial rows. A pair of ribs run more or less parallel ca. one-quarter of the way in from the rim and three-fourths from the axial thickening, thinning at the ends of the plate-scale. Spine-scales are cylindrical, 10-13 µm long, bipartite, consisting of a shaft and base plate; shaft straight, ca.0.2 µm thick, hollow; periphery with a narrow rim.

Habitat: Freshwater; ditch in the Pearl River National Wildlife Reserve Management area, St. Tammany Parish, Louisiana.

Remarks: A. dürrschmidtidae is easily distinguished from the closely related Acanthocystis granulata Dürrschmidt by the well-developed radial slits next to the median thickening. In A. granulata, the radial slits are positioned near the margin and its plate-scales also lack the nearly marginal parallel ribs. In Acanthocystis pertusa Dürrschmidt, while there are radial slits close to median thickening, its plate-scales lack both the scattered granules and marginal ribs.