Cosmarium speciosum
image © Alfred van Geest

Cosmarium speciosum. Notice crenate cell margin, rather shallow sinus and semi-elliptical outline of semicells.
Cell dimensions (L x B): 56 x 35 µm





 


Desmid of the month
September 2026

Cosmarium speciosum


Cosmarium speciosum should be compared to C. rostafinskii (Desmid of June 2025). Both species are characterized by crenulate cells, a relatively shallow sinus and longitudinal series of granules (often partially fused into ridges) just above the isthmus. However, whereas semicells of C. rostafinskii are trapeziform in outline, those of C. speciosum are semi-elliptical. In the Netherlands, Cosmarium speciosum is of incidental occurrence in shallow, mesotrophic puddles and on wet substrates.

Cosmarium speciosum
images © Marien van Westen (mouse-over) 10 µm mark

Empty cell of Cosmarium speciosum showing a coarsely punctate wall, concentric series of intramarginal, bipartite verrucae and a transversal, supraisthmial band of longitudinal ridges.