Phylum: Charophyta   Family: Desmidiaceae

Micrasterias rotata  J. Ralfs 1848

A large subspherical cell with the polar lobes protruding and all lobes are denticulate. It is similar to Micrasterias denticulata Ralfs 1848, which can be found in the same samples but, bizarrely, lacks dentition on the lobe endings.
Cell dimensions: L: 239-295 µm; B: 216-262 µm; Is: 38-47 µm; L/B: 1.09-1.20.
West & West (1905: 102) note: “… is not a common species, although very widely distributed.” The status in the Outer Hebrides still reflects the Wests’ observations. However, it can be locally abundant. Found in acidic mesotrophic waters such as moorland pools and abandoned peat-cuttings.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Van Westen, M.C. (2024). Sieralgen in Drenthe.
West, W. & West, G.S. (1905). A Monograph of the British Desmidiaceae, Volume 2.