Phylum: Charophyta   Family: Desmidiacea

Staurastrum pingue E. Teiling 1942

This is similar to S. planctonicum but smaller. There is no overlap in cell-body length and the isthmus is also smaller but there may be a slight overlap. Coesel & Meesters (2013) consider S. planctonicum a variety of S. pingue and separate them on isthmus breadth: less than 10 µm in S. pingue and greater than 10 µm in var. planctonicum. This precise distinction doesn’t fit data from the Outer Hebrides, so I prefer to follow Van Westen’s (2024) lead and regard then as separate species. The processes are usually slightly divergent but can be parallel.
Cell dimensions: L: (body): 31-34 µm L: (overall): 31-38 µm; B: 47-55 µm; Is: 6.9-8.1 µm; L/B: (overall): 0.6-0.7.
Less common than S. planctonicum, found in circumneutral to slightly acidic waters, such as in the plankton of lochs and marginal vegetation of moorland pools.

References: 
Van Westen, M.C. (2024).Sieralgen in Drenthe.