Stauroneis alegrensis Guerrero & Vouilloud, 2025

Stauroneis alegrensis Guerrero & Vouilloud sp. nov.

LM ( Figs 1–22 View FIGURES 1–22 ): Frustules rectangular in girdle view, with valve face flat and intercalary bands clearly punctate ( Figs 1–6 View FIGURES 1–22 ). Valves lanceolate with convex margins and obtusely rounded apices, slightly protracted in some specimens ( Figs 7–22 View FIGURES 1–22 ). Valve dimensions (n=40): length 115–180 µm, width 22–33 µm, length/width ratio 4.5–6.2. Prominent pseudoseptum present at each pole ( Figs 1, 3, 5, 12, 16, 20 View FIGURES 1–22 ). Axial area moderately broad, slightly widening towards central area. Central area forming bow-tie shaped stauros, sometimes widening asymmetrically towards the margins. Raphe lateral except at valve ends where it becomes filiform. Central raphe endings deflected near the central area and terminating in elongated, expanded central pores. Terminal raphe fissures bent in the same direction. Striae radiate throughout length of the valve, 17–19 (20) in 10 µm, composed of coarse, clearly discernible areolae, 14–17 (18) in 10 µm. Shortened, marginal striae at central area not observed.

SEM ( Figs 23–34 View FIGURES 23–28 View FIGURES 29–34 ): Striae uniseriate composed of round to mostly transapically elongated areolae, continuous onto the valve mantle; areolae at valve face/mantle junction more distantly spaced and irregularly arranged ( Figs 24, 25 View FIGURES 23–28 ). Valve margins occupied by broad, non-areolated area ( Fig. 23 View FIGURES 23–28 ). Central raphe endings deflected with widened tear-drop central pores ( Fig. 24 View FIGURES 23–28 ). Terminal raphe fissures bent and sickle-shaped onto mantle ( Fig. 25 View FIGURES 23–28 ). Internally, raphe fissures linear, flanked at both sides by longitudinal thickenings except at central area and near poles ( Figs 26–27 View FIGURES 23–28 ). Stauros well-developed and thickened ( Figs 26, 28 View FIGURES 23–28 , 29, 31, 32 View FIGURES 29–34 ). Central raphe endings slightly bent and not expanded ( Figs 28 View FIGURES 23–28 , 31, 32 View FIGURES 29–34 ); distal endings not visible due to presence of pseudoseptum ( Figs 27 View FIGURES 23–28 , 30 View FIGURES 29–34 ). Areolae occluded by hymenes rectangular in shape ( Fig. 32 View FIGURES 29–34 ). When areola occlusions are detached, interstriae elevated over round to elliptical internal areola openings ( Fig. 28 View FIGURES 23–28 ). Valvocopula open, ornamented with double row of round to elongated or irregularly shaped poroids, internally expanded at both poles forming a small septum covering the pseudoseptum ( Figs 29, 30, 33, 34 View FIGURES 29–34 ).

Type: — ARGENTINA. Misiones: Departamento Cainguás, Aristóbulo del Valle, Salto Alegre, 27.131°S, 54.828°W, J. Simonato, 20 May 2019 ( holotype LPC! slide 15616(2), represented by the specimen in Figs 19–20 View FIGURES 1–22 , England finder: L/22–3).

Habitat: —On epilithic mosses. At sampling time, the water of the nearby fall had a temperature of 19.4 °C, a pH of 7.1, a conductivity of 0.04 mS cm-1, and a concentration of TDS of 0.02 mg L- 1.

Etymology: —The specific epithet refers to the type locality Salto Alegre, Misiones, where the sample was collected.