Stauroneis fuegiana Casa & Van de Vijver, 2017

Casa, Valeria, Mataloni, Gabriela & Vijver, Bart Van De, 2017, Stauroneis fuegiana, a new Stauroneis species (Bacillariophyta) from Tierra del Fuego, southern Argentina, Phytotaxa 311 (1), pp. 85-92 : 86-88

Stauroneis fuegiana Casa & Van de Vijver sp. nov. ( Figs 1–13 )

LM ( Figs 1–7 ): Valves rather broadly lanceolate, never linear-lanceolate with clearly convex margins, gradually tapering towards the weakly protracted, subrostrate apices. Valve dimensions (n=25): length 95–165 μm, width 17– 25 μm, length/width ratio 5.7–6.3. Axial area narrow, strictly linear, almost 1/5 of the total valve width, gradually widening until the central area. Central area forming a rectangular, only weakly wedge-shapedly widened stauros. Shortened striae only rarely present in the central area. Raphe clearly lateral. Branches straight with clearly deflected to weakly hooked ( Figs 6, 7 ), droplike expanded proximal raphe endings and hooked terminal raphe fissures. Striae clearly radiate throughout the entire valve, 16–18 in 10 μm. Areolae clearly discernible in LM, 18–20 in 10 μm. Occasionally, narrow hyaline line visible at the valve face/mantle junction ( Fig. 1 , arrows). SEM ( Figs 8–13 ): Striae uniseriate composed of transapically elongated areolae ( Figs 9, 10 ). Striae continuing uninterruptedly onto the mantle ( Fig. 10 ). External proximal raphe endings clearly deflected terminating in large, droplike expanded pores ( Fig. 9 ). Small silica ridge bordering the raphe ( Figs 8, 9 ). Terminal raphe fissures strongly hooked, continuing onto the mantle ( Fig. 10 ). Narrow silica ridge present near the central area at the valve face/mantle junction, not continuing up to the apices ( Fig. 9 , arrows). Internally, stauros well-developed ( Fig. 11 ). Internal proximal raphe endings terminating on the stauros ( Fig. 12 ). Distal raphe endings terminating on small helictoglossae ( Fig. 13 ). Stria foramina transapically elongated ( Fig. 12 ).

Type:—Rancho Hambre, Tierra del Fuego, ARGENTINA: sample RH-VP4- SED, V. Casa, 21/11/2016 (holotype BR! slide no. 4480, isotype PLP! slide 325, University of Antwerp, Belgium).

Ecology and distribution:— Stauroneis fuegiana is regularly observed in the peat bogs pools of Tierra del Fuego. It is possible that the species has been identified in the past as S. phoenicenteron or S. gracilis . The species is usually found in sediment and moss samples from several shallow, dystrophic, acid to slightly acid (pH 3,6–6,8) waterbodies with low conductivity (<200 μS/cm) and DOC ranging between 5,1 to 35,1 mg/l.

Etymology:—The specific epithet fuegiana refers to the type locality in Tierra del Fuego.

Figures

FIGURES 1–7. Stauroneis fuegiana sp. nov. Type population from Rancho Hambre, Tierra del Fuego (sample RH-VP4-SED) (1–5) LM views of an entire valve. The arrows in Fig. 1 indicate the marginal crest on the valve face/mantle junction (6–7) LM views of the central area with the deflected proximal raphe endings. Scale bars represent 10 μm.

FIGURES 8–13. Stauroneis fuegiana sp. nov. Type population from Rancho Hambre, Tierra del Fuego (sample RH-VP4-SED) (8) SEM external view of an entire valve. (9) SEM external detail of the central area showing the deflected proximal raphe endings. The arrows indicate the marginal crest. (10) External detail of the valve apex showing the terminal raphe fissures. (11) SEM internal view of an entire valve. (12) SEM internal detail of the central area with the well-developed stauros and the proximal raphe endings. (13) Internal detail of the valve apex with a distal raphe endings and the helictoglossa. Scale bars represent 10 μm.