Navicula membranacea Cleve;Stauropsis membranacea (Cleve) Meunier; Stauroneis membranacea (Cleve) Hustedt.
Pavillard, 1925: p. 61, Fig. 109 (as Navicula membranacea); Cupp, 1943: p. 193, Fig. 142 (as Navicula membranacea); Hendey, 1964: p. 221, Pl. XXI: 3 (as Stauroneis membranacea); Simonsen, 1974: p. 40 (as Stauroneis membranacea); Throndsen et al., 2007: p. 188.
Cells delicate, thin-walled united into short, straight chains; 30-50 µm wide. In girdle view rectangular; valves flat or slightly concave in the center, with a thickening in the middle at right angles to the raphe. In valve view, cells are narrow elliptical and acute. Girdle zone striated; no structure is visible. Central nodule dilated into a narrow stauros that reaches to the margin. Notches at point of union of valve mantle and girdle. Chromatophores two, drawn out like a ribbon. Several pyrenoids are present (Cupp, 1943).
Cells length 60-75 µm; width 38-46 µm.
Neritic, truly planktonic species of wide distribution.
Sites of occurrence in RSA:
In Winter 2006 Cruise, this species was observed at various sites (refer sites map), often in large numbers; maximum abundance (3.4*10^3 cells/l) was associated with the Iranian coast in the central part of the inner RSA (St. 27). It has been previously reported (as Stauroneis membranacea) from the inner RSA (Simonsen, 1974) and from Kuwaiti waters (Al-Yamani et al., 2004; Al-Kandari et al., 2009).