Phylum: Charophyta Family: Desmidiaceae
Cosmarium turpinii Brébisson
Apparently quite common in circumneutral waters but more sampling is needed in the Outer Hebrides to establish its status. A distinct character is the adjacent twin protuberances which occasionally merge into one
References:
West, W. & West, G.S. (1908) A Monograph of the British Desmidiaceae, Volume 3
Kouwets, F.A.C. (in manuscript) European Flora of the Desmid Genus Cosmarium
Coesel, P.F.M. & Meesters, K.J. (2007) Mesotaeniaceae and Desmidiaceae of the European Lowlands