Phylum: Charophyta   Family: Desmidiaceae

Staurastrum teliferum  J. Ralfs 1848

This is superficially similar to S. gladiosum but that species has a less open sinus, as opposed to the acute-angled sinus in S. teliferum. In apical view the sides are almost straight in S. teliferum but concave in S. gladiosum. Also, the L/B ratio (without spines) of S. gladiosum is less than 1.1, while that of S. teliferum is greater than 1.1. A final difference is in the ecology; S. teliferum is an acidophile mainly found in oligotrophic waters whereas S. gladiosum prefers circumneutral to slightly alkaline habitats. Most of these distinctions are from Van Westen (2024).
Cell dimensions: L: 32-39 µm; B: 25-34 µm; Is: 10-13 µm; Sp: 4-6.5 µm; Overall LxB: 37-42 x 34-42; L/B minus spines: 1.14-1.34.
Zygospore dimensions: minus projections: 29-33 µm; overall: 59-62 µm; projections: 14-16 µm.
A common acidophile in bogs and loch margins especially in the plankton.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Van Westen, M.C. (2024). Sieralgen in Drenthe.
West, W., West, G.S. & Carter, N. (1923). A Monograph of the British Desmidiaceae, Volume 5.