Family: Lithodesmiaceae H. and M. Péragallo emend Simonsen
Genus: Streptotheca Shrubsole (=Heliotheca Ricard)
Scientific name: Streptotheca indica Karsten
Cells extremely flat, with square outline, sometimes three-cornered; united by valve faces,leaving very little, if any, aperture. Cell wall very weakly siliceous; chains strongly twisted;valves narrowly elliptical with a rudimentary central knob. Chromatophores are numerous small granules (Cupp, 1943). A second generic name published by Ricard (1987), Heliotheca, is a validly published substitute name for Streptotheca Shrubsole 1890 (type: S. tamesis Shrubsole). However, Streptotheca Shrubsole remains currently used (Round et al., 1990).
Allen and Cupp, 1935: p. 143, Fig. 77; Crosby and Wood, 1958: p. 512, Pl. 36: 33.
Cells in chains, united by valves which have a slight central depression; tripartite in valve view, twisted on pervalvar axis. Dimensions: 200 50 20 µm (Crosby and Wood, 1958).
Cells length 100-110 µm; width 70-80 µm.
Typical species in tropical areas of the Indian Ocean (Allen and Cupp, 1935). It has been reported also from Australia and New Zealand (Crosby and Wood, 1958).
Sites of occurrence in RSA:
In Winter 2006 Cruise, this species occurred at few scattered sites (refer sites map), usually in small numbers; however, it was quite abundant at some localities; maximum abundance (1.9*10^3 cells/l) was recorded in the Sea of Oman (St. 98).