G.Karst. (Karsten, 1905: 104, pl. 13, figs 11–17)
Corethron criophilum “inerme” phase (G.Karst.) Hendey (1937: 329, pl. viii, fig. 9) Corethron criophilum f. inerme (G.Karst.) Hasle (1969: 83)
Hustedt (1958: 131), Priddle & Fryxell (1985: 54, figs A, B), Thomas & Bonham (1990: 105, pl. 12, figs 2, 4, 6), Crawford et al. (1998: 11, figs 3, 44–59)
Cells chain-forming, weakly silicified, cylindrical; pervalvar axis 40–350 µm. Valves weakly convex, circular; apical axis 20–62 µm; only end cells of colonies with dissimilar valves; intercalary valves with short spines interlocking siblings. Upper valve of terminal cell bearing 2 types of spines around margin (one long and barbed, the other short and hooked); hook with a distinct terminal projection at right-angles to the spine and 3 thinner projections below and closely appressed to the spine (Fig. b). Lower valve with a marginal ring of barbed spines; spines T-shaped at their base, inserted into sockets on valve margin. Prior to cell division, spines held within the parent cingulum (girdle) all point in the same direction; cells free of cingulum have barbed spines orientated downwards and hooked spines orientated upwards. Cingulum composed of half-bands (Fig. f).
Near Davis Station, East Antarctica; Antarctic inshore waters (Hasle, 1969); South Georgia and Enderby Land (Hendey, 1937); Antarctic circumpolar distribution (Thomas & Bonham, 1990).