Cosmarium humile. Notice semicells consisting of a broad, at the lateral margins somewhat undulate basal part and a smaller, rectangular apical part. Notice also the apical series of granules causing a regularly crenate outline of the apex.

Cell dimensions (L x B): 25 x 22 µm



Desmid of the month
February 2018

Cosmarium humile

C. humile is one of the many small-sized Cosmaria the cell wall of which is sculptured by both incurvations and granules. C. humile may be recognized in that the lateral sides of the semicells show a deep subapical incurvation dividing the semicell in a broad basal part and a smaller, rectangular apical part. Cell wall is provided with a central tubercle and a number of marginal and intramarginal granules the expression of which may widely vary. In particular the apical series of granules cause a regularly crenate appearance of the semicell outline. In the Netherlands, C. humile is a rather common species in various kinds of circumneutral, meso-eutrophic water bodies.

Empty semicell of C. humile in top view showing the apical pattern of granulation.



SEM picture of Cosmarium humile. Notice (flattened) central tubercle as well as  series of (intra)marginal granules (white dots represent mucilaginous pore excretions).

SEM picture of another cell of C. humile marked by a more expressed cell wall sculpturing.