Phylum: Charophyta   Family: Desmidiaceae

Cosmarium quadrifarium P.M. Lundell 1871

A striking desmid with a series of blunt, emarginate granules around the periphery in face view. In apical view, these granules amount to a series of 4 rows. A central protuberance has about 14 granules in an approximate circle. It should be compared with the similar, but slightly larger, C. hexastichum Lundell 1871. However, that species has 6 rows of granules when viewed apically.
Single cell dimensions: L. 42 µm; B. 35.3 µm; Is. 16.2 µm; Th. 24.4 µm; L/B. 1.19.
A widespread but seemingly rare species found in the tychoplankton of lochans and pools, also found in mountainous regions.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium. Part 1: Text. Part 2: Plates.