Ditylim brightwellii (West) Grunow ex Van Heurck

Division: Chromophyta
Class: Bacillariophyceae
Order: Biddulphiales
Suborder: Biddulphiineae
Family: Lithodesmiaceae H. and M. Péragallo emend Simonsen
Genus: Ditylum Bailey
Scientific name: Ditylim brightwellii (West) Grunow ex Van Heurck

Cells elongated, prismatic to box-shaped. Solitary, except immediately after division. Valves three- to four cornered, seldom bipolar, with a strong central siliceous hollow spine, and a marginal ridge, strengthened by ribs. Intercalary bands, more or less numerous. Valve surface more or less waved, with usually poorly developed humps on the corners. In the central part, a usually three-cornered elevated region, the margin often has a circle of short pervalvardirected spines. Outer valve margin more or less strongly waved, giving the appearance of lines running from valve to valve. Cell wall weakly siliceous; valve membrane, delicately areolated-punctated. Chromatophores are numerous and small (Cupp, 1943).


Synonyms:
Triceratium brightwellii West; Ditylum trigonum Bailey; Ditylum inaequale Bailey

References:
Pavillard, 1925: p. 53, Fig. 91; Hustedt, 1930: p. 786, Figs. 457-459; Cupp, 1943: p. 148, Fig. 107-A, 107-B; Crosby and Wood, 1958: p. 510, Pl. 36: 27; Hendey, 1964: p. 111, Pl. V: 1; Ricard, 1987: p. 219, Figs. 552-554;Throndsen et al., 2007: p. 181 .

Description:
Cells triangular in space; somewhat like a prism; angles often rounded, giving a cylindrical appearance. Cells three to eight times longer than broad. Valves small, undulate, furnished with a corona of short, but stout spines surrounding one large central spine. Central spine straight; central area of valve often raised, hyaline. Girdle elongated. Lebour (1930) described the connecting zone as composed of scale-like intercalary bands. Chromatophores: numerous cocciform bodies, usually grouped toward the center of the cell. Cells very weakly siliceous; diameter of valve 28-46 m; pervalvar axis 80-130 m; length of spine 20-50 m (Hendey, 1964).

Dimensions:
Cells length 85-103 µm; diameter 28-32 µm.

Distribution:
Neritic, south temperate species.

Sites of occurrence in RSA:
In Winter 2006 Cruise, this species occurred at few sites (refer sites map), usually in small numbers; however, it was quite abundant at some localities; maximum abundance (1.8*10^3cells/l) was recorded off Qatar (St. 43). It has been previously reported from Kuwaiti waters of the inner RSA (Al-Yamani et al., 2004; Al-Kandari et al., 2009).