Phylum: Charophyta   Family: Desmidiaceae

Hyalotheca dissiliens var. minor  Delponte

Recorded as less common that the nominate variety on the continent, but little data available for Britain to make an assessment

References: 
Coesel, P.F.M. & Meesters, K.J. (2007) Mesotaeniaceae and Desmidiaceae of the European Lowlands