Cosmarium nasutum. Notice semicells with a trapeziform-semicircular outline and deeply crenate margin, the apex being 2-crenate. Crenations provided with conical granules.

Cell dimensions (L x B): 35 x 30 µm



Desmid of the month
November 2022

Cosmarium nasutum

C. nasutum is a characteristic, granulate Cosmarium species marked by trapeziform-semicircular semicells with a deeply crenate margin. The apex is 2-crenate with a median indentation. Just above the isthmus the cell wall is furnished with an emarginate wart and usually above that wart one or two transversal bands of 6-8 smaller granules may be distinguished. The supraisthmial ornamentation is separated from radiate series of intramarginal granules by an unsculptured zone. Zygospores are globose and provided with rather long, furcate spines. In the Netherlands, C. nasutum is a rare species, occurring on wet, sandy substrates.

Image © Marien van Westen

Empty cell of C. nasutum showing characteristic ornamentation: an emarginate wart at the isthmus and a transversal series of smaller granules above it. Moreover, radiate series of intramarginal granules.

Zygospore of C. nasutum. Notice spines being furcate at the apex and conical at the base (provided with a ring of denticulations) .