Phylum: Charophyta   Family: Desmidiaceae

Cosmarium thwaitesii J. Ralfs 1848

A large cell about twice as long as broad with a narrow, wide-open, sinus. Cell-wall smooth covered with fine pores.
Single cell dimensions: L: 52.8 µm; B: 26.3 µm; Is: 23.1 µm; Th: L/B: 2.01.
Widespread but rarely recorded. Thought originally to be associated with circumneutral water, it is now regarded as being more tolerant of acidic conditions.

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