Cells living singly or forming star-shaped colonies, zigzag bands, or bunches, united to one another by a gelatinous cushion on the end of the cell. In girdle view narrow linear.Intercalary bands and septa are absent. In valve view linear or slightly lancet-shaped ends,unlike. Valve borders similar to those of preceding genus, often beset with small spines;
valve surface with short marginal striae or structureless. Chromatophores are more or less numerous small granules. Pelagic marine forms. This genus contains the longest diatoms known at the present time; often present in large masses in the plankton (Cupp, 1943).
Scientific name: Thalassiothrix frauenfeldii Grunow
Pavillard, 1925: p. 59, Fig. 106 A; Allen and Cupp, 1935: p.153, Fig. 97; Cupp, 1943: p. 185, Fig. 135; Hendey, 1964: p.165; Simonsen, 1974: p. 37, Pl. 24: 4.
Cells united into star-shaped colonies or zigzag bands; in girdle view linear. Valves very narrow linear, ends distinct,
but only slightly unlike; one end blunt-rounded, near the other end usually widened then decreased to form a wedge-shaped point. Valves 90-210 µm long; 2-4 µm wide. Marginal spines small but regular, 6-9 in 10 µm. Valves are otherwise structureless (Cupp, 1943).
Cells length 110-140 µm; width 3-4 µm.
Oceanic, south temperate species; widespread distribution.
Sites of occurrence in RSA:
In Winter 2006 Cruise, this species was commonly observed at various sites (refer sites map),often in large numbers; maximum abundance (3.6 103 cells/l) was associated with the central part of the inner RSA (St. 43). Species has been previously reported from the inner RSA (Simonsen, 1974) and from Kuwaiti waters (Al-Yamani et al., 2004; Al-Kandari et al., 2009).