Phylum: Charophyta   Family: Desmidiaceae

Staurastrum longipes  (C.F.O. Nordstedt) E. Teiling 1946

The semicells are broadly campanulate with a wide open sinus that has an acute indent. The long processes are tipped with four stout spines. Mainly 3- and 4-radiate but 5-radiate have been recorded.
Overall cell dimensions: L: 75-85 µm; B: 80-119 µm; Is: 7.5-9.5 µm.
West, West & Carter (1923: 104) as St. paradoxum var. longipes, record this species as common in the plankton over much of Britain. These days it’s regarded as scarce and confined largely to the Atlantic regions.

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.