Family: Lithodesmiaceae H. and M. Péragallo emend Simonsen
Genus: Streptotheca Shrubsole (=Heliotheca Ricard)
Scientific name: Streptotheca tamesis Shrubsole
Helicotheca tamesis (thamensis) (Shrubsole) Ricard
Pavillard, 1925: p. 53, Fig. 90; Hustedt, 1930: p. 780,Fig. 455; Cupp, 1943: p. 148, Fig. 106; Crosby and Wood, 1958: p. 512, Pl. 36: 32; Hendey, 1964: p. 113, Pl. VII: 2; Ricard, 1987: p. 219, Figs. 549, 550 (as Helicotheca tamesis); Throndsen et al., 2007: p. 182 (as Helicotheca tamesis).
Cells twisted so that chains are spiral; one end of cell in relation to the other twisted about 90°. Cells almost flat, square. Apical axis 60-98 µm long. Valves not quite flat but, with two deeply placed knobs which fit into corresponding depressions in the adjacent cells. Nucleus central. Chromatophores numerous, small roundish plates, more or less radiate in the cell (Cupp, 1943).
Cells length 140-160 µm; width 120-140 µm.
Sites of occurrence in RSA:
In Winter 2006 Cruise, this species occurred at various sites (refer sites map), usually in small numbers; maximum abundance (1.4*10^2 cells/l) was recorded in the Sea of Oman (St. 88). It has been previously reported from Kuwaiti waters of the inner RSA (Al-Yamani et al., 2004; Al-Kandari et al., 2009, as Helicotheca thamensis).