Stauroneis cavalcantei Tremarin, Tusset & T. Ludwig, 2018

Tusset, Eduardo A., Tremarin, Priscila I. & Ludwig, Thelma A. V., 2018, Two new Stauroneis species (Bacillariophyta, Stauroneidaceae) from midwestern karstic Brazilian formations, Phytotaxa 358 (3), pp. 265-277 : 269-272

Stauroneis cavalcantei Tremarin, Tusset & T. Ludwig sp. nov. ( Figs 11‒22 )

Valves lanceolate, 73.0‒110.5 μm long and 12.5‒17.5 μm wide (n=20), with subtly protracted apices. Pseudosepta absent. Raphe sternum linear. Raphe lateral, becoming filiform at proximal ends. Proximal raphe endings externally with drop-like central pores, and internally straight, delicate. External distal raphe endings hooked to secondary side, and internally terminate in small helictoglossae. Stauros narrow, nearly rectangular, slightly expanded towards valve margins. Short striae occasionally present in central area. Striae uniseriate, radiate throughout, 20‒22 in 10 μm. Areolae rounded, 26‒30 in 10 μm.

Type:— BRAZIL. Mato Grosso do Sul: Miranda, channel of the Miranda River, São Francisco farm, epiphyton on Eichhornia sp. , 20°09’01.1’’S, 56°50’08.9”W, September 2013, P. I. Tremarin & K. P. Cavalcante s.n. (holotype UPCB! 78276—here depicted in Fig. 12 ).

Etymology: the species is dedicated to our colleague Dr. Kaoli Pereira Cavalcante, from the University of Vale do Acaraú, Ceará, Brazil.

Stauroneis cavalcantei is similar to S. fuegiana Casa & Van de Vijver (2017: 86) , S. valeriana Metzeltin et al. (2005: 227) , and S. heinii Lange-Bertalot & Krammer (1999: 91) in relation to lanceolate outline of the valves, striation pattern and rectangular stauros ( Table 2). However, these species differ from S. cavalcantei by having larger valves with lower densities of striae and areolae. Moreover, S. fuegiana has transapically elongated areolae and a marginal crest discernible in LM ( Casa et al. 2017). A marginal crest was not seen in S. cavalcantei (see fig. 20).

Stauroneis gracilis Ehrenberg (1843: 386) also resembles S. cavalcantei but the elliptic-lanceolate valves, broader stauros and lower areolae density ( Table 2) from the former, distinguish them. Besides, the proximal raphe endings of S. heinii are strongly reverse-lateral, the pore is inflated and curved to the secondary valve side, and S. gracilis are curved ( Lange-Bertalot & Genkal 1999), not straight as in S. cavalcantei . Stauroneis supergracilis Van de Vijer & Lange-Bertalot (in Van de Vijver et al. 2004: 73) and S. angustilancea Lange-Bertalot & Metzeltin in Werum & Lange-Bertalot (2004: 175) have narrowly lanceolate valves, and lower density of areolae and striae ( Table 2).

Metzeltin & Lange-Bertalot (1998) misidentified an exemplar from Calado Lake, Brazil (pl. 98, fig. 4), corresponding to Stauroneis cavalcantei , as S. angustilancea .

Figures

FIGURES 11‒16. Stauroneis cavalcantei Tremarin, Tusset & T. Ludwig sp. nov. LM. Valve views. Fig. 12. UPCB 78276 (holotype specimen). Scale bar = 10 μm.

FIGURES 17‒22. Stauroneis cavalcantei Tremarin, Tusset & T. Ludwig sp. nov. SEM. Figs 17‒18. External and internal valve view, respectively. Figs 19. Internal view of central area showing the stauros and the proximal raphe endings. Fig. 20. External view of central area showing the striation pattern and the proximal raphe endings. Fig. 21. Internal view of valve apex, note the helictoglossa. Fig. 22. External view of valve apex showing the distal raphe endings. Scale bars = 5 μm (Figs 19, 20), 2 μm (Figs 17, 18, 21, 22).