(Ehrenb.) Simonsen (1982: 105, figs 1–9)
Charcotia actinochilus (Ehrenb.) Hust. (Hustedt, 1958: 126, figs 57–80)See Simonsen (1982: 105–106) for full synonymy.
Coscinodiscus actinochilus Ehrenb. (Ehrenberg, 1844b: 200; 1854: pl. 35A, figs xxi, 5)
Villareal & Fryxell (1983: 461, figs 21–32), Priddle & Fryxell (1985: 102, figs A–C), Everitt & Thomas (1986: 5, fig. 2B), Moisan & Fryxell (1993: 493), Fryxell (1990: 112, tab. 14.1, fig. 1)
Cells solitary, cylindrical to discoid. Valves flat with rounded edges, 20–112 µm diameter. Areolae in isolated radial rows that are sometimes curved or incomplete; areolation variable; areolae 5–11 in 10 µm, loculate, with a foramen on the inside, bordered by a thickened rim (Fig. e, f). Marginal labiate processes 1 in 10 µm, 9–15 µm apart, laterally expanded (Fig. e, f). Pseudonodulus sometimes present near junction of flat part of valve face and mantle, not perforate. Striae on valve mantle 13–21 in 10 µm. Chloroplasts numerous, discoid.
Coastal waters near Davis Station, East Antarctica (Everitt & Thomas, 1986); Weddell Sea (Moisan & Fryxell, 1993); Weddell-Scotia Sea (Garrison et al., 1987); Indian Ocean sector of the Antarctic (Kopczyńska et al., 1986); Kerguelen and Atlantic sectors of the Antarctic, very common from 68°49’S 0°40’W to 69°43’S 06°30’E, and 69°43’S 06°30’E to 61°32’S 0°00’ (Hustedt, 1958); coastal waters off Syowa Station, East Antarctica (Ishikawa et al., 2001).
Specimens recorded from near Davis Station have a diameter range of 24–52 µm.
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).