Stauroneis karstica Tusset, Tremarin & 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 : 272-274

Stauroneis karstica Tusset, Tremarin & T. Ludwig sp. nov. ( Figs 23‒47)

Frustules rectangular in girdle view, 10.0‒12.0 μm wide. Valves rhombical-lanceolate to lanceolate in smaller forms, 21.0‒56.5 μm long and 5.5‒12 μm wide (n=30), with attenuate to acutely rounded apices, not protracted. Pseudosepta reduced. Raphe sternum lanceolate to linear in smaller specimens. Raphe filiform. External and internal proximal raphe endings straight, not expanded. External distal raphe endings nearly straight, extending on mantle, and internally terminate in small helictoglossae. Stauros bow-tie-shaped. Short striae occasionally present in central area. Striae uniseriate, radiate at center, becoming slightly convergent towards apices, 12‒14 in 10 μm. Areolae rounded to transapically elongate, (16) 20‒30 in 10 μm, internally occluded by hymenes. At apices, areolae apically elongated and depressed between prominent longitudinal-oriented apical ribs. Girdle composed of 2‒3 open bands perforated by two rows of poroids.

Type:— BRAZIL. Mato Grosso do Sul: Bodoquena, da Lontra pool, epiphyton, 20°43’53.1’’S, 56°43’38.7”W, September 2013, P.I. Tremarin & K.P. Cavalcante s.n. (holotype UPCB! 78275—here depicted in Fig. 23).

Etymology: the species was named in homage to the environment in which the species was found, in the Brazilian Karst.

Paratypes: — BRAZIL. Mato Grosso do Sul: Bonito, Formoso River UPCB! 76099 ; Mato Grosso do Sul: Bonito, Sucuri River , UPCB! 76100 ; Mato Grosso do Sul: Bonito, Chapeninha stream, UPCB! 78227 ; Mato Grosso do Sul: Bonito, Perdido River , UPCB! 78231 ; Mato Grosso do Sul: Jardim , Olho d’ Água, UPCB! 78233 ; Mato Grosso do Sul: Bodoquena, Boca da Onça waterfall, UPCB! 78240 ; Mato Grosso do Sul: Jardim , da Prata River, UPCB! 78245 ; Mato Grosso do Sul: Bonito, waterfall in Chapena River , UPCB! 78248 ; Mato Grosso do Sul: Bonito , waterfall in Sitio Ybirá Pe farm, UPCB! 78254 ; Mato Grosso do Sul: Bonito , waterfall in Sitio Ybirá Pe farm, UPCB! 78255 ; Mato Grosso do Sul: Bonito, Formoso River , UPCB! 78256 .

Stauroneis karstica is very distinct from any other Stauroneis species. The rhombical-lanceolate valves, longitudinal-oriented ribs near the apices, bow-tie shaped stauros, rounded to transapically elongate areolae, reduced pseudosepta, and unexpanded central pores distinguish the species. The valve outline and stauros shape resemble those of Stauroneis acuta W. Smith (1853: 59) . However, S. acuta has broadly rounded (not attenuated) apices, lateral raphe with inflated central pores, prominent pseudosepta, and larger valves ( Table 3).

The areolae crossed by longitudinal-oriented ribs are also recorded with S. stodderi Lewis (1865: 13‒14) , S. staurolineata Reimer (1961: 206‒207) , and S. amica Lange-Bertalot et al. (2003: 126) . However the ribs extend all the way through the valve surface, sometimes crossing the fascia, rather than located only in the apical region. The ultrastructural details of S. stodderi were documented by Siver et al. (2005).

Stauroneis karstica was found in lotic environments with neutral to slightly alkaline waters (pH 7.2‒8.0) and moderate conductivity (323‒476 μS/cm).