Spirotaenia beijerinckii Coesel (2002: 72) (Figs. 5, 12)

Cells 5–8 times longer than wide, fusiform with narrowly apices, chloroplast ribbon-shaped, parietal, constituted by a single loosely twisted helical ribbon, with two tiny reddish dots at each end. Cell length 25–42 μm, breadth 4.5–5 μm.

Material examined: Brazil, Bahia State, municipality of Uruçuca, Serra Grande, Parque Estadual Serra do Conduru, 20/IV/2023, 14°29’36” S 39°08’13” W, B. F . Souza (HUESC 26220) .

Ecology: pond; periphyton associated to aquatic macrophytes, including Eleocharis sp.; abiotic variables of water: pH 6.4, temperature 32.4 ºC, conductivity 24 μS/cm, TDS 12 ppm, ORP 177 mV.

Distribution: Europe: Netherlands, Germany, United Kingdom (Brook & Williamson 2011, Guiry & Guiry 2023); South America: Brazil (present study).

Note: Spirotaenia beijerinckii is a species that has only been documented in northern hemisphere countries so far. It typically inhabits oligotrophic and shallow environments characterized by acidic conditions (Coesel & Meesters 2007). Its prominent characteristic is the presence of two small red dots at each end of the chloroplast. This coloration may lead to confusion with S. erythrocephala, which can be distinguished by its more rounded cell poles and a continuously reddish chloroplast end, lacking the two small red dots found in S. beijerinckii .