G.A.Fryxell & Semina (1981: 442, figs 1–10)
Fryxell (1990: 112, pl. 14.1, fig. 2), Hasle & Syvertsen (1997: 122)
Cells solitary, cylindrical. Valves circular, flattened, with a high mantle and a thin delicate fringing skirt that partly overlaps the first girdle band; apical axis 6.5–15 µm. Areolae in irregular radial rows, sometimes fasciculate, 12–18 in 10 µm in the centre, 21–24 in 10 µm towards the margin. Labiate processes slightly expanded, 3–5 per valve, located on mantle, c. 1 µm long and laterally expanded (viewed from inside of valve). Pseudonodulus sometimes visible, possibly areolate.
Southern Ocean, south of Australia; type locality, Southern Indian Ocean, 46°04.7’S 49°19.0’E (Fryxell & Semina, 1981); Antarctic and sub-Antarctic (Fryxell, 1990).
Species of Actinocyclus have the following diagnostic features: radial, usually fasciculate areolation; a marginal ring of labiate processes, laterally expanded internally; a marginal pseudonodulus (sometimes difficult to distinguish); and radial, hyaline bands (see Villareal & Fryxell, 1983 and Watkins & Fryxell, 1986 for further details).