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Authority

O.G.Kozlova (1964: 168, pl. 1, fig. 5)

Class

Diatomophyceae

Order

Centrales

Family

Thalassiosiraceae

Synonyms

N/A

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Basionym

N/A

Additional References

Kozlova (1967: 58–59, fig. 6), Fryxell & Hasle (1979b: 19–20, figs 25–30), Johansen & Fryxell (1985: 161, figs 6, 64), Fryxell & Johansen (1990: 99, pl. 11.8, fig. 2)

Description

Cells chain-forming by means of a chitinous strand from the central strutted process(es) (Fig. e, f), usually heavily silicified; inter-cell distance at least twice the length of the pervalvar axis. Valves circular, 12–25 µm diameter, those of smaller cells slightly concave; marginal striae 15–18 in 10 µm. Areolation eccentric; areolae 7–16 in 10 µm in the centre, increasing to 9–18 in 10 µm near the margin, loculate, opening externally via a simple foramen and internally via a finely pored velum. Strutted processes 1 or 2 in the valve centre, a single ring of processes at the margin (Fig. d, arrows), 1–3 in 10 µm; processes with internal extensions having tricolumnar supports. Labiate process solitary, simple, with a tangential orientation to the internal opening. In small cells the single labiate process is usually 3 or 4 areolae away from the central strutted process. For a complete description, see Hasle & Fryxell (1979b).

Distribution

Coastal waters off Davis Station, East Antarctica; type locality, Indian Ocean sector of the Antarctic (Kozlova, 1964); south-western Atlantic (Johansen & Fryxell, 1985).

Comments

Areolation has been reported as irregular to linear (Fryxell & Hasle, 1979b) or irregular to eccentric (Johansen & Fryxell, 1985). The densities of areolae in our material (7–10 in 10 µm in the centre, 12–13 near the margin) varies slightly from those reported by others: 7–16 in 10 µm in the centre (Johansen & Fryxell, 1985) and 9–13 (Fryxell & Hasle, 1979b) or 15–18 (Johansen & Fryxell, 1985) near the margin. A lower density of marginal, strutted processes (1–2 in 10 µm) was reported by Fryxell & Hasle (1979b) and Johansen & Fryxell (1985). Moreover, Johansen & Fryxell (1985) described the strutted processes having internal extensions with tricolumnar supports, one of the features that distinguishes this species from the closely related T. frenguelliopsis which has operculate strutted processes. Marginal areolar density is typically greater (24–30 in 10 µm) in T. frenguelliopsis.

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