Phylum: Charophyta   Family: Desmidiaceae

Staurastrum elongatum J. Barker 1869

A striking cell that can’t be confused with any other. The extended middle section of the semicells have concave sides and an enlarged basal ‘bulb’ encircled with three rows of small denticulations. Predominantly triradiate, the processes are relatively short and divergent, tipped with about 5 small spines.
Cell dimensions: L: 71-75 µm; B: 19-22 µm; Is: 9.2-10.9 µm; Proc: 18-20; L/B: 3.28-3.85; Overall LxB: 76-83 x 46-58.
Found in slightly acidic, mesotrophic, waters such as moorland pools and bogs. A rare desmid with only one site in the Outer Hebrides as of 2025, where it was moderately abundant. Taken from squeezed Sphagnum and algal sludge.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
West, W., West, G.S. & Carter, N. (1923). A Monograph of the British Desmidiaceae, Volume 5.