Phylum: Charophyta   Family: Desmidiaceae

Cosmocladium perissum J. Roy & J.P. Bisset 1894

Cells small, nearly as broad as long, sinus deep and opening widely. Side-view elliptical, chloroplast axile with a single pyrenoid. The cells are loosely joined by very delicate gelatinous threads, which are hard to seen in the light microscope. Usually no more than four cells are found together and then in a single profile. Roy & Bisset (1894: 254) describe the zygospore as: “… large in proportion to the fronds, extremely irregular in shape, and reddish-brown in colour. Grows apparently in free groups.”
Cell dimensions: L: 11-13 µm; B: 10-12 µm; Is: 5.9-7 µm; Th: 5-7 µm; L/B: 1.09-1.3.
Found in mesotrophic, circumneutral waters but rarely recorded.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Van Westen, M.C. (2024). Sieralgen in Drenthe.