Desmid of the month
March 2009

Cosmarium subpunctulatum*

Cells of Cosmarium subpunctulatum are moderate in size, almost as broad as long and marked by a linear, closed sinus. Semicells are trapeziform with broadly rounded angles and slightly convex lateral sides. Cell wall ornamentation consists of a more or less circular group of granules in the centre of the semicell separated from radiate series of intramarginal/marginal granules by an unsculptured zone. The globose zygospores are furnished with furcate spines. C. subpunctulatum is widely distributed and occurs in both slightly acidic, mesotrophic and alkaline, meso-eutrophic waters. Zygospores are rather rare.

* C. subpunctulatum is a synonym of C. punctulatum var. subpunctulatum

Image © Marien van Westen

Cosmarium subpunctulatum. Notice the subquadrate cell shape and the granulate outline.

Cell dimensions (L x B): 30 x 28 µm

C. subpunctulatum cell in somewhat oblique position showing that granules cover most of the cell surface.

Image © Henk Schulp

Image: Hanny Kooijman-van Blokland © IBED

Dead, empty cell of C. subpunctulatum showing the pattern of cell wall granulation.

SEM picture of C. subpunctulatum. Notice the unsculptured zone in between the central group of granules and the radiate series of intramarginal granules.

Zygospore of C. subpunctulatum. Notice that the spines are furcate at the apex and have a ring of small teeth at the top of their conical base (mouse over).

Image © Henk Schulp (mouse over)