Cells are as long as wide or slightly longer then wide; cells of strain ATWS01-1 are 33.9 ± 2.1 µm (min 30 µm, max 38 µm, n = 20) wide and 36 ± 2.34 µm (min 32 µm, max 40 µm, n = 20) long. Cell contains many golden brown elongated chloroplasts and a horseshoe-shaped nucleus located in the equatorial part of the cell. The epicone is helmet-shaped and the hypocone roughly trapezoidal. The cingulum is descending about one cingular height. The sulcus broadens in its antapical portion and is delimited on both sides by moderately developed sulcal lists. The cell surface is smooth and ornamented with many scattered small pores. The plate formula is: Po, 4’, 6’’, 5C, 8-10S, 5’’’, 2’’’’. Po is ornamented by several small pores and presents a comma-shaped foramen. A connecting pore is generally not present on Po. Plate 1’ is irregularly rhomboidal, with longer apical right and antapical left sides; in its apical portion, it contacts the Po and in its antapical portion it contacts plate Sa. The ventral pore along the margin between Plate 1’ and 4’ is generally present. Plate 6’’ is as wide as tall or slightly wider than tall. Plate 2’’’’ variable: it can be transversally extended (prevalent type) or dorsoventrally extended, but transitions exist. Plate sp is pentagonal, and its length:width ratio is ∼1; a connecting pore is generally not present on sp. Cells are almost always single, rarely found in chains of two cells in cultures. The cyst is ellipsoidal, with a granular dark brown content and is surrounded by a mucous layer. Isolates are non-toxic. D1-D2 LSU (GenBank KF908805), ITS/5.8S (GenBank KF908813), and SSU (GenBank KF908799).

Body_length: 32-40 µm
Body_width: 30-38 µm