Desmid of the month
August 2009

Cosmarium ovale

C. ovale is a most conspicuous Cosmarium species. Its large cells (measuring up to over 200 micrometer) cannot be confused with any other European representative of this genus. Semicells are pyramidal in outline and marked by marginal and intramarginal series of conical granules. The parietal chloroplast consists of some four plates incorporating quite a number of smaller pyrenoids each. In the Netherlands, records of C. ovale are only known from some mesotrophic moorland pools dating from the first half of the last century (all pictures herewith presented are after Czech material).

Image: Cell of Cosmarium ovale. Notice the pyramidal outline of the semicells, the marginal series of conical granules and the large cell size.

Cell dimensions (L x B): 225 x 130 µm

Cosmarium ovale

Image ©Jan Šťastný



M0609tsjech_2050serie-5
Images (5) © Wim van Egmond ( multifocus mouse over © Alfred van Geest) Cell surface marked by cell wall pores Parietal chloroplast plates with thickening ridges (darker green) and globular pyrenoides Outline (rather vague) of central vacuole Granulate cell outline Concentration of crystals in central vacuole

Optical section of a cell of C. ovale showing parietal chloroplast plates with many pyrenoids. Notice accumulation of crystals in the interior (the vacuole) of the semicells.

 

 

 

 

Empty semicell of C. ovale showing coarse cell wall pores in the centre and conical granules near the margin.

 

 

Cosmarium ovale close up
 Images © Henk Schulp (mouse over) Cosmarium ovale Cosmarium ovale Cosmarium ovale Cosmarium ovale Cosmarium ovale

 

Cosmarium ovale, SEM image
SEM image © Jan Šťastný

SEM image of Cosmarium ovale.