Family: Naviculaceae Kützing
Genus: Plagiotropis Pfitzer emend Paddock
Scientific name: Plagiotropis lepidoptera (Gregory) Kuntze
Valves similar to those of Navicula, but very convex. Lanceolate, acute, usually with a wing or longitudinal band on one or both sides. Median line straight, not sigmoid, on a central or excentric keel; raphe at edge of keel. Axial area is not evident. Central area small, sometimes transverse. Striae transverse and longitudinal, punctuate; girdle zone simple. Chromatophores are either two or four plates, serrated or indented. Pyrenoids are present. Chromatophores on the girdle band as in most naviculoid diatoms (Cupp, 1943).
Tropidoneis lepidoptera (Gregory) Cleve; Amphiprora lepidoptera Gregory
Cupp, 1943: p. 197, Fig. 149 (as Tropidoneis lepidoptera); Hendey, 1964: p. 256, Pl. XXXVI: 2, 4 (as Tropidoneis lepidoptera); Hendey, 1970: p. 149 (as Tropidoneis lepidoptera); Ricard, 1987: p. 253, Figs. 843-851; Witkowski et al., 2000: p.338, Pl. 174: 1, 2.
Cells rectangular, linear-oblong, constricted in the middle. Valves lanceolate, acute or apiculate; central area small or transversely lanceolate. Wing is unilateral, projecting above the central nodule. Striae transverse; length of valves 200-350 μm (Cupp, 1943).
Cells length 180-220 µm; width 30-32 µm; transapical striae 20-21 in 10 µm.
Littoral species, but reported occasionally in the plankton.
Sites of occurrence in RSA:
In Winter 2006 Cruise, this species was observed at various sites (refer sites map), although never in large numbers; maximum abundance (4.3*10^2 cells/l) was associated with the Strait of Hormuz (St. 14a). It has been previously reported (as Tropidoneis lepidoptera) from Kuwaiti shore (Hendey, 1970) and coastal waters (Al-Kandari et al., 2009).