(G.Karst.) Hust. (VanLand.) G.A.Fryxell & Hasle (1979a: 384–386, figs 23–28)
Thalassiosira delicatula auct. non Ostenfeld (1908), sensu Hustedt (1958: 110, figs 8–10)
Thalassiosira expecta VanLand. (VanLandingham, 1978: 3995)
Johansen & Fryxell (1985: 170, figs 8, 60–63), Hasle & Syvertsen (1997: 83, pl. 12)
Cells solitary or chain-forming, discoid, heavily silicified, with a thin chitinous strand from the central strutted process. Valves flat, circular, 7–26 µm diameter. Areolation radial, coarse; areolae 14–15 in 10 µm in the centre, 16–20 in 10 µm towards the margin, loculate, opening externally via a simple foramen and internally via a finely pored velum. Strutted process solitary in valve centre or off-centre, with a single ring of processes at the margin, 3–4 in 10 µm; processes with internal extensions, operculate. Labiate process solitary, located c. one-third the distance from margin to valve centre.
Widely distributed in Antarctic waters (Johansen & Fryxell, 1985).
Only slight differences in valve diameter and areolar density separate var. expecta from the type variety.