Many Desmids are very tiny, often smaller than 1/20th of a
millimetre. They should be observed with strong magnification, 40X objectives
or more. The determination of species is not easy, sometimes it is even
hard to decide to what genus a desmid belongs. Clues for determination
of the species are the ornamentation, the shape of the cell (even the
angle of the curves)
Cosmarium species have no extensions or spikes but in many species the cell wall is covered with small bumps.
Cosmarium