Phylum: Charophyta   Family: Desmidiaceae

Cosmarium connatum J. Ralfs 1848

A large cell with a wide-open sinus, furcoid chloroplast and usually two pyrenoids. Similar, but smaller, taxa are C. pseudoconnatum Nordstedt 1870 and C. meneghinianum (Nägeli) Kouwets 2025, which has multiple pyrenoids.
Single cell dimensions: L: 86-98 µm. B: 63-74 µm. Is: 50-58 µm. L/B: 1.30-1.41.
Widespread and fairly common circumneutral to alkaline waters favouring loch-margins and moorland pools.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium.