Phylum: Charophyta   Family: Desmidiaceae

Cosmarium hexastichum P.M. Lundell 1871

Described by Lundell in 1871 at the same time as his similar C. quadrifarium Lundell 1871. The main difference being the number of rows of warts in lateral view: six in the first, 4 in the latter. His rather precise drawing depicts nine emarginate isthmial warts in two rows. Later finds have shown 7-9 warts in a less orderly configuration. The Lewis find has seven rather amorphous warts.
Single cell dimensions: L: 51.5 µm; B: 41 µm; Is: 18.5 µm; Th: 29.9 µm; L/B: 1.26.
Although regarded as widespread in Europe, it’s rarely recorded. The single Outer Hebridean find was from a slightly acidic, mesotrophic, loch.

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