Empty cell of C. venustum (var. excavatum). Punctation of cell wall refers to scrobicles.

Cosmarium venustum

Cell dimensions (L x B): 25 x 20 µm

 

 

Desmid of the month
March 2010

Cosmarium venustum

Cosmarium venustum is a small-sized, rather inconspicuous species. In rough outline, semicells are trapeziform with an undulation about half-way the lateral sides. The cell wall is smooth but, particularly in empty cells, shows a marked scrobiculation. Usually, of C. venustum its variety excavatum is encountered which is characterized by an extra large pit in the centre of the semicell. In the Netherlands, it is a rather common species in acidic, oligotrophic bog pools.

SEM picture of C. venustum var. excavatum. Notice pattern of scrobicles and the extra large pit in the centre of the semicell characteristic of this variety.

SEM picture of C. venustum var. excavatum. Detail of central semicell region showing cell wall pores in and next to scrobicles.