Sellaphora gracillima Zidarova, Kopalová & Van de Vijver, 2016

Zidarova, Ralitsa, Kopalová, Kateřina & Vijver, Bart Van De, 2016, Ten new Bacillariophyta species from James Ross Island and the South Shetland Islands (Maritime Antarctic Region), Phytotaxa 272 (1), pp. 37-62 : 51-52

Sellaphora gracillima Zidarova, Kopalová & Van de Vijver , sp. nov. ( Figs 157–177 )

LM observations ( Figs 157–174 ): Valves linear to linear-elliptic with almost parallel or weakly convex valve margins. Apices non protracted, broadly rounded. Valve dimensions (n=25): length: 8.5–14.0 μm, width 2.5–3.5 μm. Axial area very narrow, linear. Central area moderately large, transapically elongated, rounded ( Fig. 157 ) to rectangular ( Fig. 172 ) but often asymmetrical in shape due to several (2–5) irregularly shortened striae. Raphe filiform with straight, indistinct proximal raphe endings. Distal raphe endings not discernible in LM. Striae fine, radiate throughout the entire valve, 30–32 in 10 μm. Striae near the central area weakly curved. Areolae not visible in LM. SEM observations ( Figs 175–177 ): Externally, valve face flat ( Figs 175, 177 ). External raphe branches straight to slightly curved ( Fig. 175 ). Proximal raphe endings weakly and gradually expanded, almost straight to weakly unilaterally deflected ( Fig. 175 ). Distal raphe fissures elongated, hooked opposite the proximal raphe endings, continuing onto the mantle beyond the last striae ( Fig. 175 ). Striae uniseriate, composed of small rounded areolae, shortly extending onto the mantle to just below the valve face/mantle junction ( Figs 175, 177 ). Areolae near the axial area slightly larger than the others ( Fig. 175 ). Open foramina present at the apices ( Fig. 175 ). Internally ( Fig. 176 ), raphe straight. Proximal raphe endings terminating on a thickened central nodule, weakly deflected. Distal raphe endings terminating onto weakly developed helictoglossae. Internal areolar openings rounded, covered by individual, porous hymenes ( Fig. 176 ). Shallow depressions present at both valve apices ( Fig. 176 ). Girdle composed of 2 open copulae, the valcocopula bearing a single row of small rounded poroids ( Fig. 177 ).

Type: — ANTARCTICA. South Shetland Islands: Livingston Island, Byers Peninsula, sample BY049 (62° 38’ 43.1” S, 61° 02’ 22.9” W, 75 m a.s.l.), B. Van de Vijver, 14 January 2009 (holotype BR! 4458, isotype PLP! 312).

Etymology: —The specific epithet ‘ gracillima ’ refers to the fine striation of the species.

Ecology and confirmed distribution: — Sellaphora gracillima has been probably reported in the past as Eolimna (Navicula) minima (Grunow in Van Heurck 1880: 107) Lange-Bertalot in Moser et al. (1998: 153) or as Navicula tantula Hustedt (1943: 162) on several localities in the Maritime Antarctic Region ( Kellogg & Kellogg 2002, Kopalová & Van de Vijver 2013, Kopalová et al. 2013, 2014, Sterken et al. 2015, figs 3AX, AY). So far, it is only with certainty present on Livingston Island, South Shetland Islands. The largest population was observed in a lake situated on the main central plateau on Byers Peninsula, next to Limnopolar Lake at an altitude of 75 m. The lake has a pH of 7.6 with a conductivity value of 60 μS/cm. Both nutrient and mineral levels are quite low ( Kopalová & Van de Vijver 2013).

Figures

FIGURES 157–177. Sellaphora gracillima sp. nov. LM and most of the SEM pictures taken from the holotype population (sample BY049) from Livingston Island (South Shetland Islands).157–174. LM views of 18 valves from the type population.175. SEM of an entire valve, external view. 176. SEM of an entire valve, internal view. 177. SEM of an entire valve, showing the valve mantle and girdle (picture taken from Livingston Island, sample BY051). Scale bar represents 10 μm except for figs 175–177 where scale bar = 5 μm.