Phylum: Charophyta   Family: Desmidiaceae

Cosmarium desectum (R.L. Grönblad) F.A.C. Kouwets 2025

A very small cell with widely gaping sinuses, broadly rounded sides and truncate apices. Chloroplast axile with one pyrenoid, occasionally just one pyrenoid per cell.
Cell dimensions (2): L: 8.7-8.9 µm, B: 8.6-9.6 µm, Is: 6.8-6.9 µm; Th: 6.3-6.5 µm, L/B: 1.04-0.91.
An acidophile found in moorland pools and bogs. Its status in the Outer Hebrides is unclear.

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