Family: Rhizosoleniaceae De Toni
Genus: Rhizosolenia (Ehrenberg) Brightwell
Scientific name: Rhizosolenia hebetata f. semispina (Hensen) Cleve
Rhizosolenia semispina Hensen
Pavillard, 1925: p. 32, Figs. 48, 49 (as Rhizosolenia semispina); Hustedt, 1930: p. 591, Fig. 338; Allen and Cupp, 1935: p. 129, Fig. 42; Crosby and Wood, 1958: p. 522, Pl. 39: 73 b; Hendey, 1964: p. 150, Pl. III: 5; Simonsen, 1974: p. 29; Priddle and Fryxell, 1985: p. 86-87; Ricard, 1987: p. 173, Fig. 230; Throndsen et al., 2007: p. 161.
Cells cylindrical; valves, conical, very finely striate and produced to terminate in a long slender spine. Spine usually straight or only slightly curved, and processing an internal basal cavity. Cirdle composed of two dorsiventral lines of intercalarly scale-like plates, scales almost rhombic, but presenting the appearance of a zigzag line when the cell offers a lateral aspect. The scales at the base of the valve are often clearly marked with an elongated depression which corresponds to the spine of the neighboring cell. Diameter of valve 5-12 µm (Hendey, 1964).
Cells length 250-330 µm; diameter 7-8 µm.
Oceanic form; common in all sub-tropical and temperate waters.
Sites of occurrence in RSA:
In Winter 2006 Cruise, this species was commonly observed at various sites (refer sites map),often in large numbers; maximum abundance (3.3*10^4 cells/l) was associated with the central part of the inner RSA (St. 36). It has been previously reported from the inner RSA (Simonsen, 1974) and from Kuwaiti waters (Al-Yamani et al., 2004).