B.C.Booth H.J.Marchant, in Booth & Marchant (1987: 255, figs 34 (holotype), 35, 36)
Cells planktonic, solitary, non-motile, spherical, 3–3.6 µm diameter. Cell wall comprising 8 siliceous plates: 3 shield plates, 1 ventral plate, 1 keeled triradiate plate keel and 3 girdle plates; junctions between plates distinctively raised; all plates lacking veins and papillae. Shield plates circular, 1.7–2 µm diameter, slightly convex, smooth, with a raised margin, 1–3 short processes sometimes present in centre of plate. Ventral plate convex, 2.4–2.6 µm diameter, with a slightly raised rim, an irregular spathulate central process and/or a concentric ring of processes that may be dichotomously branched. Triradiate plate arms 1.4–1.7 µm long; triradiate keel sometimes well developed, with a slightly raised margin; plate slightly convex. Girdle plates with pronounced keels; processes irregularly shaped, sometimes dichotomously branched, c. 2 µm long. Ornamentation of plates, including the number and placement of processes and their length, can vary.
Widely distributed in Antarctic waters; Weddell Sea (Silver et al., 1980); south of Australia (Nishida, 1986); Prydz Bay, East Antarctica, (Marchant & McEldowney, 1986).