H.J.Marchant, in Booth & Marchant (1987: 258, figs 6 (holotype), 7)
Buck & Garrison (1983: 1275, fig. 35, as a siliceous cyst), Takahashi et al. (1986: 87, figs 17, 18, as “Cyst 4A”)
Cells planktonic, solitary, non-motile, spherical or subspherical, 5–5.8 µm diameter. Cell wall comprising 5 siliceous plates: 3 round plates and 2 triradiate plates. Round plates of unequal size, 3.6–4.6 µm diameter, slightly convex, with or without rounded spathulate or dichotomously branched processes (3 µm long) arising from the rims and centre of the plate. Triradiate plates with raised margins, some with processes 1.5 µm long, with or without a central process 1.8 µm long. Margins between triradiate and shield plates distinct; margins between triradiate plates difficult to observe. Ornamentation of the plates can vary.
Prydz Bay, East Antarctica; Terra Nova Bay, Ross Sea; Weddell Sea (Silver et al., 1980; Buck & Garrison, 1983); Kita-no-seto Strait, near Syowa Station, East Antarctica (Takahashi et al., 1986).