B.C.Booth, in Booth & Marchant (1987: 256, figs 40 (holotype), 41, 42)
Booth et al. (1981: 68, figs 24–30, as “Cyst III”)
Cells planktonic, solitary, non-motile, hemispherical, 3.1–3.8 µm diameter, c. 2.8 µm long; dorsal surface convex; ventral surface flat. Cell wall comprising 8 siliceous plates: 3 shield plates, 1 ventral plate, 1 triradiate plate and 3 girdle plates; junctions between plates usually indistinct; all plates bearing similar processes to 1.5 µm long, straight or forked, round in transverse section. Shield plates round, rarely concave, 1.8–2.8 µm diameter, with delicate radiating striae. Ventral plate flat, 2.4–3.3 µm diameter, with delicate radiating striae. Triradiate plate without a keel; arms 1.4–2.3 µm long. Girdle plates with scattered processes, each with 2 straight or forked spines to 9 µm long.
Sub-Arctic Pacific and Antarctica (Booth & Marchant, 1987).
Little morphological variation has been observed in this species, but Booth & Marchant (1987) reported that Antarctic cells had straight spines on the girdle plates in contrast to the branched spines of sub-Arctic material.