Phylum: Charophyta   Family: Desmidiaceae

Cosmarium nymannianum A. Grunow 1868

Semicells broadly pyramidal with the basal half broadly rounded. Upper sides are concave with a truncate, retuse apex. There is a large scrobiculus in the centre. A characteristic species not easily confused with other taxa.
Cell dimensions: L: 44.9-49.5 µm; B: 33.7-36.3 µm; Is: 8.3-10.6; Th: c.24 µm; L/B: 1.28-1.41.
Widespread and locally common in acidic moorland bogs and loch-margins, often with Sphagnum.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium. Part 1: Text. Part 2: Plates.
West, W. & West, G.S. (1905). A Monograph of the British Desmidiaceae, Volume 2.