Phylum: Charophyta   Family: Desmidiaceae

Actinotaenium didymocarpum (P.M. Lundell) P.F.M. Coesel & A. Delfos 1986

First described by Lundell (1871: 85, pl. 5: 9) as Penium didymocarpum, later moved to Actinotaenium by Coesel & Delfos (1986: 364, figs. 1-4, 29-31). Cells cylindric with the sinus barely visible. Apices truncately rounded, chloroplast asteroid with one pyrenoid.
Cell dimensions: L: 30-43 µm; B: 12-18 µm; L/B: 2.20-2.70. An acidophile of moorland pools and bogs.
Note: From Coesel & Meesters (2023: 70): “A didymocarpum, in the concept of Coesel & Delfos, is quite near to A. diplosporum. Actually, it cannot be reliably distinguished from A. diplosporum var. minus as described by Teiling (1954).

References: 
Coesel, P.F.M. & Delfos, A. (1986) New and interesting cases of conjugating desmids from Lapland.
Coesel, P.F.M. & Meesters, K.J. (2023 second edition) Desmids of the Lowlands.
Lundell, P.M. (1871) De Desmidiaceis, quae in Suecia inventae sunt, observationes criticae.
Ruzicka, J. (1981) Die Desmidiaceen Mitteleuropas, Volume 1, Part 2.
Teiling, E. (1954) Actinotaenium, genus Desmidiacearum resuscitatum.