(Cleve) Hasle, in Hasle & Syvertsen (1997: 161, pl. 31)
Rhizosolenia antarctica G.Karst. (Karsten, 1905: 95, pl. 11, fig. 1; fide Hasle, 1969), Manguin (1960: 265, pl. 4, figs 56, 57)
Rhizosolenia cylindrus Cleve (1897: 24, pl. 2, fig. 12)
Priddle & Fryxell (1985: 84, figs A, B), Priddle et al. (1990: 120, pl. 15.4, figs 1, 2, as Rhizosolenia cylindrus), Sundström (1986: 103, figs 276–278)
Cells in long straight chains that break readily, weakly silicified, cylindrical; pervalvar axis up to 300 µm. Valves flat or slightly convex, circular; apical axis 8–50 µm; rows of fine areolae radiating from central external process tube; process hollow, curved to attach to adjacent cell (Fig. b); process tube, as well as the impression upon the adjacent cell into which the tube fits, both visible by LM. Girdle composed of numerous open (split) bands with ligulae and antiligulae, with fine poroid areolae in a rectangular arrangement. Chloroplasts numerous, stellate.
Prydz Bay, coastal waters near Davis Station, East Antarctica; Terre Adélie (Manguin, 1960, as R. antarctica); Heard I. (Manguin, 1954, as R. antarctica); Weddell-Scotia Confluence (Garrison et al., 1987).
The closely related Guinardia flaccida (Castrac.) H.Perag. has a distribution that is “cosmopolitan, but not seen in polar waters” (Hasle & Syvertsen, 1997). Our most southerly record of this species was at 44°09.51’S 147°13.83’E.