Family: Chaetocerotaceae Ralfs in Pritchard
Genus: Chaetoceros Ehrenberg
Scientific name: Chaetoceros coarctatus Lauder
Chaetoceros rudis Cleve
Hustedt, 1930: p. 656, Fig. 370; Allen and Cupp, 1935: p.134, Fig. 52; Cupp, 1943: p. 107, Fig. 62; Crosby and Wood, 1958: p. 514, Pl. 37: 38; Hendey, 1964: p. 121, Pl.XII: 1; Simonsen, 1974: p. 30.
Cells cylindrical, elliptical in valve view. Chains long,robust in appearance, with two ends markedly different,30-44 µm wide; apertures very small. Valve surface flat, with rather high mantle, one-third to two-thirds of the apical axis. More or less deep, but always distinct constriction at suture between mantle and girdle band; posterior terminal setae large, strongly curved, heavily spined, shorter than others; anterior terminal setae less robust, curved toward posterior end, spined less heavily; setae in center of chain curved like anterior terminal setae, spined; setae with rows of fine puncta running lengthwise visible usually only on posterior terminal setae where they occur in double rows. Usually found with a species of Vorticella (probably Vorticella oceanica) attached, sometimes in large numbers (Cupp, 1943).
Apical axis 28-33 µm; pervalvar axis 32-35 µm.
Distribution: Oceanic, tropical or subtropical species.
Sites of occurrence in RSA:
In Winter 2006 Cruise, this species was frequently observed at various sites (refer sites map),often in large numbers; maximum abundance (2.7*10^3 cells/l) was associated with the Strait of Hormuz (St. 16a). It has been previously reported from the inner RSA (Simonsen, 1974) and from Kuwaiti waters (Al-Yamani et al., 2004; Al-Kandari et al., 2009).