Phylum: Charophyta   Family: Desmidiaceae

Actinotaenium cucurbita (J. Ralfs) E. Teiling 1954

First described by Ralfs as Cosmarium cucurbita (1848: 108, pl. 17: 7). Later, Teiling (1954: 406, fig. 66) transferred it to Actinotaenium. Teiling sums up the species variability: “Brebisson’s main type is cylindrical with abruptly retuse ends but the attenuate type with more conical semicells and slightly rounded ends may lie quite as prominent. Within these two types there is a great variation in the proportions and the size.” The cell-wall is uniformly marked with medium pores.
Cell dimensions: L: 38-56 µm; B: 21–28 µm; L/B: 1.80-2.10.
An acidophile of moorland bogs, especially with Sphagnum.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition) Desmids of the Lowlands.
Ralfs, J. (1848) The British Desmidieae.
Ruzicka, J. (1981) Die Desmidiaceen Mitteleuropas, Volume 1, Part 2.
Teiling, E. (1954) Actinotaenium, genus Desmidiacearum resuscitatum.