Family: Chaetocerotaceae Ralfs in Pritchard
Genus: Chaetoceros Ehrenberg
Scientific name: Chaetoceros tortissimus Gran
Hustedt, 1930: p. 751, Fig. 434; Cupp, 1943: p. 142, Fig. 99; Hendey, 1964: p. 135, Pl. XI: 2;Ricard, 1987: p. 207, Fig. 483.
Chains straight or slightly bent, loose, very strongly curved around chain axis, without distinct terminal setae. Cells 14-20 µm broad. Setae thin, arising a little way inside corners, about at right angles to chain axis, going in all directions. Cell wall weakly siliceous; cells in broad girdle view rounded-rectangular; valves with slightly convex valve surface, touching in the middle, not at corners, therefore apertures are apparent only at corners. No notch at margin of girdle band. Chromatophores one, lying in girdle region. Resting spores unknown (Cupp, 1943).
Apical axis 21 -25 µm; pervalvar axis 9-11 µm.
Neritic, temperate species.
Sites of occurrence in RSA:
In Winter 2006 Cruise, this species was observed at various sites (refer sites map), often in very large numbers. It was recorded as bloom-forming at some localities; blooms with cells concentration more than 10^6 cells/l were associated with the Strait of Hormuz area and the southern part of the inner RSA (Stations 14a, 56, and 70). It has been previously reported from Kuwaiti waters of the inner RSA (Al-Yamani et al., 2004; Al-Kandari et al., 2009).