Pinnularia quesadae Van de Vijver & Zidarova 2011, sp. nov.

Pinnularia quesadae Van de Vijver & Zidarova, sp. nov. (Figs 51–56)

Valvae lanceolatae marginibus convexis apicibusque potius late rotundatis, non protractis. Crista marginalis cingens valvae. Dimensiones (n=12): longitudo 24.0– 35.5 µm, latitudo 8.7–9.6 µm. Area axialis moderate lata, linearislanceolata, dilatans in aream centralem. Area centralis parva ad paene absens, rectangularis. Fascia abest. Raphe lateralis ramis externis positis in crista axiali leviter elevate, claro discernenda in microscopico photonico. Terminationes proximales unilateraliter deflexae, ad poros centrales deflectae in latere opposite. Fissurae distales unciformes. Crista axialis connexa in apices crista marginali. Striae transapicales latae, paene parallelae ad leviter radiatae, fere aequidistantes omnino, 6–7 in 10 µm. Striae compositae seriebus nonnulis pororum parvorum, individualiter tectorum.

Valves lanceolate with convex valve margins and rather broadly rounded, non protracted apices. Marginal raised rim surrounding entire valve. Valve dimensions (n=12): length 24.0– 35.5 µm, width 8.7–9.6 µm. Axial area moderately broad, linear-lanceolate, widening towards central area. Central area small, in some cases almost absent (Fig. 8), rectangular, bordered by 1–2 short striae. Raphe lateral with outer raphe branches curved, located on weakly raised rim, clearly visible in LM. Proximal raphe endings unilaterally deflected, pore-like, near pores weakly turned to other side. Distal fissures sickle-shaped. Axial rim connected near apices, marginal rim with raphe fissures continuing on marginal rim (Fig. 56). Transapical striae broad, almost parallel to weakly radiate, nearly equidistant throughout entire valve, 6–7 in 10 µm. Striae composed of several rows of small pores, obscured individually by outer covering.

Type:— Byers Peninsula, Livingston Island, South Shetland Islands, sample BY67, Leg. B. Van de Vijver, coll. date 18/01/2009, slide no. BR-4237 (holotype BR), slide PLP-187 (isotype University of Antwerp, Belgium), slide BRM-7/100 (isotype BRM).

Habitat and Distribution:— Pinnularia quesadae is a rare species on Livingston Island and so far only found together with P. perlanceolata and P. borealis var. pseudolanceolata (see above) in a large, circumneutral (pH 7.3) shallow pool on Byers Peninsula surrounded by fellfields and moss vegetations, growing into the water.

Etymology:—Named for Prof. Dr. Antonio Quesada (Universidad Autónoma de Madrid), one of the leading scientists in the Byers Peninsula research and one of the principal investigators of the Limnopolar project on this Peninsula.

Observations:— Pinnularia quesadae is at present the only member of the Distantes group with a raphe located on an axial raised rim. Based on valve outline and dimensions, P. quesadae may be confused with P. borealis var. pseudolanceolata, but the presence of the rim and the less radiate striation pattern should prevent misidentification (Table 1). Pinnularia perlanceolata has valves that are clearly wider (10.6–12.8 µm vs. 8.7– 9.6 µm) with a more elliptic-lanceolate valve outline, lower number of striae (5–6 vs. 6–7 in 10 µm in P. quesadae) and an almost straight raphe with straight to weakly deflected central endings.