Phylum: Charophyta   Family: Desmidiaceae

Tetmemorus granulatus J. Ralfs 1848

In the Netherlands Van Westen (2024) has found a group that fall between T. granulatus and T. leavis. They are provisionally identified as T. granulatus morpha, which may constitute a new species. I have not found this size-range in the Outer Hebrides but do have some cells of T. laevis that reach 120 µm in length, which are clearly identified by the shape of the apices. The smaller dead cell depicted below doesn’t feature in the dimensions as it was still developing.
Cell dimensions: L: 143-230 µm; B: 25-40 µm; L/B: 4.0-6.0.
This species has a similar distribution to T. laevis and equally as common in the Outer Hebrides.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Van Westen, M.C. (2024). Sieralgen in Drenthe.