Phylum: Charophyta   Family: Desmidiaceae

Cosmarium medioretusum P.F.M. Coesel 2007

One of several small, smooth-walled desmids. The main characteristics are the lateral sides have two depressions giving a three-undulate appearance. The apex is more or less truncate with a median dent. The central protuberance can vary from being quite noticeable to almost lacking.
Single cell dimensions: L: 16.3-22.1 µm; B: 15.1-18.7 µm; Is: 4.3-6.5 µm; Th: 10.2-12.9 µm; L/B: 1.19-1.30.
Status uncertain as there are few data available. Would seem to prefer circumneutral waters such as loch-margins, moorland pools and disused peat-cuttings.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium. Part 1: Text. Part 2: Plates.