Hasle & G.A.Fryxell (1977: 26–28, figs 46–53)
Herzig & Fryxell (1986: 14, tabs 1, 2)
Cells solitary. Valves flat, with a narrow mantle flaring to a broad marginal rim, 20–43 µm diameter. Areolae ±linear except where opposite the labiate process; additional rows of small areolae at the valve margin result in the marginal row curving; areolae ranging from 6–7 in 10 µm at the valve centre to 16–18 in 10 µm at the margin and 15–20 in 10 µm on the valve mantle, with areolar diameter at the margin less than half that at the centre. Areolae hexagonal, loculate, opening externally via a circular foramen, internally via a fasciculately pored velum (Fig. b). Strutted processes in a single marginal ring, 3–4 in 10 µm, with short internal extensions, operculate. Labiate process solitary, formed one areola-width nearer valve face than strutted processes, with a short internal extension orientated along the tangent. Single central process (visible by LM) causing displacement of the surrounding areolae (Fig. a). For a complete description, see Hasle & Fryxell (1977).
Macquarie I. (54°58’S 155°26’E); type locality, “South Pacific Ocean (3°05’S 02°56’S 84°48’W–84°55’W)” (Hasle & Fryxell, 1977); tropical waters of northern Chile, 18°20’S 74°16’W (Rivera, 1981); warm-temperate waters of the Gulf Stream in the North Atlantic (Herzig & Fryxell, 1986).
We have found only rare, isolated valves (but no intact cells), as was also the experience of Hasle & Fryxell (1977). The occurrence of this species near Macquarie Island is the first record for the sub-Antarctic and may indicate some mixing of subtropical and cold waters in this region (see also T. symmetrica).