Podosira stelliger Mann

Division: Chromophyta
Class: Bacillariophyceae
Order: Biddulphiales
Suborder: Coscinodiscineae
Family: Hemidiscaceae Hendey
Genus: Podosira Ehrenberg
Scientific name: Podosira stelliger (Bailey) Mann

 

Cells solitary or united in short chains. Valves circular; convex. Frustule almost elliptical in girdle view. Valve surface punctuate; umbilicus absent; girdle composed of numerous narrow intercalary bands. Chromatophores are small, granular. Cells usually fixed by means of a mucous pad to the substratum, but frequently found in plankton (Hendey, 1964).

Synonym:
Hyalodiscus stelliger Bailey

References:
Hustedt, 1930: p. 286, Fig. 128; Crosby and Wood, 1958: p. 491, Pl. 31: 5; 35: 1 (as Hyalodiscus stelliger); Hendey,1964: p. 90, Pl. XXII: 6; Simonsen, 1974: p. 8; Ricard, 1987: p. 169, Figs.191, 192.

Description:
Cells discoid; valves strongly convex, finely striate; striae moniliform. Central area of valve strongly differentiated; peripheral zone striate; striae often parallel or nearly so, fasciculate,giving the appearance of dividing the valve into sectors. Marginal zone strong, finely striate. In the central area, the puncta are few and irregularly arranged. Girdle is composed of numerous narrow intercalary bands. Chromatophores, numerous small plates. Diameter of valve 40-78 µm, pervalvar axis 15-30 µm (Hendey, 1964).

Dimensions:
Valve diameter 55-68 µm.

Distribution:
This is a bottom form that favors a high salinity medium. The cells live either singly or in short chains, attached to the substratum by a small pad of mucilage. A tychopelagic form,common in the plankton.

Sites of occurrence in RSA:
In Winter 2006 Cruise, a single specimen was observed at each site (refer sites map) in the inner RSA and the Sea of Oman. Species has been previously reported from the inner RSA (Simonsen, 1974).