B.C.Booth H.J.Marchant, in Booth & Marchant (1987: 251, figs 15 (holotype), 16–18)
Booth et al. (1981: 68, figs 31–38, as “Cyst IV”), Kosman et al. (1993: 124, figs 38–43)
Cells planktonic, solitary, non-motile, subspherical or hemispherical, 3.5–4.2 µm diameter. Cell wall comprising 8 keeled siliceous plates: 3 shield plates, 1 ventral plate, 1 triradiate plate and 3 oblong girdle plates; junctions between plates distinct; all plates with coarse venation, lacking papillae. Shield plates 1.6–2.2 µm diameter, flat to slightly convex, radially veined, with (1–) 2 (–4) central knobs. Ventral plate 2.8–3.5 µm diameter, conical or hemispherical, radially veined, with a smooth slightly raised margin; central process with 1–4 lobes. Girdle plates with a wing-like undulating keel, with a narrow raised margin and perpendicular veins on either side of keel. Triradiate plate with a triradiate keel, most pronounced midway along the arms.
Prydz Bay, East Antarctica; sub-Arctic Pacific (Booth & Marchant, 1987).