Phylum: Charophyta   Family: Desmidiaceae

Euastrum turneri 

This desmid is closest to Euastrum neospeciosum P.F.M. Coesel & K.J. Meesters 2023. It differs in having a broader polar lobe and divergent granules at the apical angles. The sides have three lobes which are all bilobulate. The Outer Hebridean population has a smaller L/B ratio, but Ruzicka (1981) gives a much great range.
Cell dimensions: L: 39.4-40.3 µm; B: 30.5-32.8 µm; Is: 9.5-10.3 µm; Th: 18.2-19.3 µm; L/B: 1.23-1.30.
Most authors describe it as an acidophile but Ruzicka (1981) notes “It prefers moderately acidic sites but can occasionally also occur in more acidic or neutral environments.” The only population from the Outer Hebrides was found in slightly alkaline conditions in semi-permanent rainwater pools. The original find was from Ireland and John & Williamson (2009) also record it there. This might suggest an Atlantic-alpine distribution. It is rarely encountered.

References: 
John, D.M. & Williamson, D.B. (2009). A Practical Guide to the Desmids of the West of Ireland.
Ruzicka, J. (1981). Die Desmidiaceen Mitteleuropas, Volume 1, Part 2.
West, W. & West, G.S. (1905). A Monograph of the British Desmidiaceae, Volume 2.