Andreoli & Moro, in Moro et al. (2002: 105, figs 1-17)
[after Moro et al. (2002)] Cells ovoid, to 8–10 µm long, 5–6 µm diameter. Body scales of 3 types: an outer rather loose layer of crown scales, a middle layer of closely fitting box scales and an inner layer of smaller scales. Crown scales c. 180 nm across the base, c. 200 nm high, with a central spine and 4 arching ribs attached near the spine tip and extending down to the base-plate. Box scales square, c. 270 nm on each side, with 16 perforations forming indistinct square subunits. Inner scales c. 150 nm long. Flagella thin, c. 8.5 µm long, with an outer layer of limulus scales and underlying rows of pentagonal scales; limulus scales c. 250 nm long, with irregular perforations; pentagonal scales c. 40 nm diameter, with a central boss. Cells with a single lobed chloroplast surrounding a central pyrenoid. A solitary posteriolateral eyespot is located near the pyrenoid.
Type locality, in sea-ice, Terra Nova Bay, Ross Sea (Moro et al., 2002).
Sym & Pienaar (1993) discussed the diagnostic characteristics of the green flagellate Pyramimonas. Cells have either 4 or 8 flagella of equal length emerging from the anterior end of the cell. Up to 7 types of non-mineralised scales cover the cell body and the flagella, and these scales are diagnostic at the species level.
Cysts spherical, 9–10 µm diameter, with a uniform covering of a single scale type not seen on the vegetative (flagellate) cell; scales spine-like, with a distinctive stellate tip.