G.A.Fryxell & J.R.Johans., in Johansen & Fryxell (1985: 168, figs 6, 67, 68, 71, 81)
Fryxell & Johansen (1990: 99, pl. 11.8, fig. 2)
Cells chain-forming, drum-shaped in girdle view. Valves circular, 12–34 µm diameter; marginal striae 24–30 in 10 µm. Areolation irregularly linear or eccentric; areolae 7.5–16 in 10 µm in the centre, increasing to 18 in 10 µm near the margin, loculate, opening externally via a simple pore with finger-like projections (Fig. b). Strutted process solitary in valve centre, a single ring of processes at the margin, 1–2 in 10 µm (Fig. c); processes with internal extensions, with opercula covering 4 basal pores (Fig. d). Labiate process solitary, located midway between centre and margin, internally slit-like (Fig. d).
Southern Ocean, south of Australia; type locality, 50°06’S 11°46’E (south-western Atlantic Ocean); sub-Antarctic (Fryxell & Johansen, 1990).
Thallasiosira frenguelliopsis is closely related to T. frenguellii, the latter having coarser marginal striae (15–18 in 10 µm) and tricolumnar support of the internal extensions of the strutted processes. Other species with similar morphology include T. gracilis var. gracilis, T. gracilis var. expecta and T. perpusilla.