Desmid of the month
December 2011

Staurastrum sexcostatum

Among the numerous Staurastrum species with arm-like processes, S. sexcostatum is relatively easily to be recognized. Cell processes are thick-set with truncate ends and furnished with some concentric series of stout, conical granules. Similar granules, usually enlarged to emarginate verrucae, extend across the semicell apex. At the base of the semicell a supraisthmial whorl of small granules can be observed. In apical view, semicells are 5- to 7-radiate, ornamented with curved series of intramarginal granules following the outline of the semicell. In the Netherlands, S. sexcostatum is of occasional occurrence in slightly acidic, mesotrophic moorland pools.

mouse over image © Alfred van Geest

5-radiate cell of S. sexcostatum in apical view. Notice series of (emarginate) intramarginal granules following the outline of the semicell.

mouse over image © Alfred van Geest

Empty 6-radiate semicell of S. sexcostatum in apical versus isthmial view. Notice supraisthmial whorl of granules.

mouse over image © Alfred van Geest

5-radiate cell of S. sexcostatum in frontal view. Notice short processes furnished with a whorl of some 7 conical granules at the truncate end.

Cell dimensions (L x B): 36 x 38 µm

mouse over image © Alfred van Geest

6-radiate cell of S. sexcostatum in frontal view