Cosmarium obtusatum. Notice faintly crenate outline of the cell.

Cell dimensions (L x B): 55 x 50 µm

SEM image of Cosmarium obtusatum



Desmid of the month
February 2017

Cosmarium obtusatum

Cosmarium obtusatum, considering cell size and shape, may be confused with C. botrytis. However, whereas cells of C. botrytis are firm-lined and for the most part equally beset with small, but distinct granules, the cell wall in C. obtusatum in its outline is faintly crenate, shows a few series of flattened verrucae just within the margin but for the most part is unsculptured. In the Netherlands, C. obtusatum is rather common in benthos and tychoplankton of various meso-eutrophic, circumneutral water bodies.

Dead cell of C. obtusatum better showing crenate margins.

Another dead, empty cell of C. obtusatum showing some intramarginal series of flattened verrucae.