Phylum: Charophyta   Family: Desmidiaceae

Cosmarium contractum sensu W & G.S. West 1905

This taxon is described in Kouwets (2025) as Cosmarium contractum Morpha 1, pending more research and more finds. I refer you to that work for a detailed analysis of this complex.
Cell dimensions: L: 37.9-46.8 µm; B: 25.4-32.7 µm; Is: 7.6-10.6 µm; Th: c.16; L/B: 1.41-1.54.
An acidophile found in oligo-mesotrophic waters such as moorland pools and lochs. Distribution is difficult to evaluate due to the complex nature of this group.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium.
West, W. & West, G.S. (1905). A Monograph of the British Desmidiaceae, Volume 2.