Spirotaenia tetrahelica G. J. P. Ramos & C. W. N. Moura 2023, sp. nov.

Spirotaenia tetrahelica G.J.P.Ramos & C.W.N.Moura, sp. nov. (Figs. 1–4, 11)

Diagnosis: Cells 6–8 times longer than wide, broadly fusiform with rounded to slightly truncated poles. chloroplast ribbon-shaped, parietal, with four spiral ribbons that merge at the cell poles, sometimes with slightly reddish or brownish coloration at the ends. Cell dimensions: length 55–77.5 μm, width 9.5–10.5 μm.

Type:— BRAZIL. Bahia: Lençóis, Lat. 12°29’04” S, Long. 41°28’23” W, 15 September 2022, G. J. P. Ramos s/n (Holotype HUESC 26222!).

Holotype:—Material numbered (HUESC 26222!) [pro parte], deposited at Herbarium of State University of Santa Cruz, population partially illustrated here (Figs. 1–4, 11).

Ecology:— puddle; metaphyton, pooled with various Cyperaceae and associated filamentous algae such as Mougeotia and Spirogyra spp.; abiotic water data: pH 4.3, temperature 25.4 ºC, conductivity 14 μS/cm, TDS 7 ppm, ORP 406 mV.

Etymology:— The epithet is due to the four spiral ribbons of the chloroplast.

Distribution: South America: Brazil (present study).

Differential diagnosis:— Spirotaenia tetrahelica differs from other species of the genus by having fusiform cells with rounded to slightly truncated poles and a chloroplast composed of four spiral ribbons that merge at the cell poles.

At first glance, Spirotaenia tetrahelica could be confused with S. diplohelica, another notable Spirotaenia species with chloroplast having more than one parietal ribbon. However, the latter species is distinguished by the presence of only two loosely spiraled ribbons that merge into a reddish-colored cap at both cell poles, and by its smaller dimensions: length 25–40 μm, breadth 6–8 μm (Coesel & Meesters 2007). Although S. tetrahelica can also have a reddish/brownish-colored cap at the chloroplast ends, in our analyzed population, this pattern was less frequent and notable compared to other species such as S. diplohelica and S. erythrocephala. Furthermore, the chloroplast ribbons in S. tetrahelica are slightly thinner than those of S. diplohelica.

In terms of morphology, S. diplohelica can still be mistaken for representatives of Tortitaenia obscura (Ralfs) Brook (1998: 146), primarily due to the presence of various helical ribbons in their chloroplasts. However, Spirotaenia species possess a parietal chloroplast forming one or more spiral ribbons, while Tortitaenia species have an axial chloroplast with multiple spiral ridges.