Cosmarium protractum. Notice 3-lobed semicells, the apex being slightly retuse, the lateral lobes about semicircular. Chloroplast with two distinct pyrenoids.

Cell dimensions (L x B): ca 40 x 40 µm

Empty cell of Cosmarium protractum in apical view. Notice prominent median inflation.



Desmid of the month
September 2014

Cosmarium protractum

C. protractum is a granulate Cosmarium species that can readily be recognized by its 3-lobed semicells. The about trapeziform apical lobe abruptly passes into semicircular lateral lobes. The centre of the semicell is distinctly inflated and ornamented with concentric series of cell wall granules. Similar granules are to be seen on the semicell lobes. In the Netherlands, Cosmarium protractum is of occasional occurrence in mesotrophic, circumneutral to sligthly alkaline water bodies, in particular in peat pits in the western part of the country.

Empty cell of Cosmarium protractum showing pattern of cell wall granules. Notice concentric series of granules in semicell centre.

Empty cell of Cosmarium protractum in oblique position showing central inflation of the semicells.