Phylum: Charophyta Family: Desmidiaceae
Cosmarium sp. (3)
There are always unknowns but some are worth airing as a useful reference source for others who may find something similar. I can only quote the ever helpful Frans Kouwets on this one: "… although some forms of C. regnellii have a central swelling, the small granule shown suggests that a very different species is at hand here. Also the apical view shows a somewhat irregular outline suggesting the presence of faint apical humps. In short: I have no idea."