Pinnularia pseudolaucensis Zidarova & Kopalová & Vijver 2012, sp.nov.

Pinnularia pseudolaucensis sp.nov. (Figs 1–19)

Valvae lineares ad lineares-lanceolatae marginibus leviter convexis, apicibus aliquando subrostratis. In speciminibus minoribus, apices paene non protracti. Longitudo 15–22 µm, latitudo 2.8–3.7 µm. Area axialis angusta, linearis, non dilatans in aream centralem. Area centralis formans fasciam rectangularem, potius latam. Raphe filiformis, ramis rectis. Terminationibus raphis proximales extensae solum leviter supra strias centrales cum poris parvis, distantibus inter se. Fissurae raphis distales non discernandae in microscopio photonico, probabiliter falcatae. Striae parallelae ad leviter radiatae in media parte valvae, moderate convergentes ad apices, 16–18 in 10 µm. Lineae speciosae longitudinales non aspectabiles in microscopo photonico.

Valves linear to narrowly linear-lanceolate with weakly convex margins and usually subrostrate apices. Smaller valves with almost non-protracted apices. Valve dimensions (n=28): length 15–22 µm, width 2.8–3.7 µm. Axial area narrow, linear, not widened towards the central area. Central area forming a rather large rectangular fascia. Raphe straight, proximal raphe endings extending only slightly beyond the last central striae. Raphe pores small and distant. Distal raphe fissures indistinct, probably sickle-shaped. Striae parallel to weakly radiate in the middle, moderately convergent towards the ends, 16–18 in 10 µm. Longitudinal lines not visible in LM.

Type:— Byers Peninsula, Livingston Island, South Shetland Islands, sample BY068, leg. B. Van de Vijver, coll. date 18/01/2009, slide no. BR-4251 (holotype BR), slide PLP-196 (isotype University of Antwerp, Belgium), slide ZU8/25 (isotype BRM).

Habitat:— The type population of P. pseudolaucensis was sampled from the sandy bottom of a small pool near the southern beaches, with an almost circumneutral pH (7.2) and a low specific conductance (<100 µS/cm) value.

Etymology:— The specific epithet refers to the close resemblance to P. laucensis Lange-Bert., Rumrich & Krammer (in Rumrich et al. 2000: 200).

Observations:— The type population of P. pseudolaucensis has a comparable valve outline and dimensions as the type of P. laucensis although the valves are somewhat narrower (width 2.8–3.7 vs 3.3–4.0 µm in the type popultion), have a higher stria density (16-18 vs 11–14 striae in 10 µm in P. laucensis) and a much smaller central area with the proximal raphe endings extending only slightly beyond the last striae. Pinnularia altiplanenis Lange-Bert., Krammer & Rumrich (in Rumrich et al. 2000: 197) differs in having a larger valve width (3.5–4.5 µm vs. 2.8–3.7 µm), as well as more radiate striae and a larger central area. Furthermore, the latter can also be separated based on its more linear outline with parallel margins. Pinnularia pseudolaucensis also resembles P. amaniana (Krammer 2000: 121) Kulikovskiy, Lange-Bert. & Metzeltin (2010: 364) but the latter is wider (4.7–6.1 µ m) with a wide axial area (Krammer 2000). Pinnularia schoenfelderi Krammer (1992: 70) is much larger (width 5–7 µm) (Krammer 2000). Other small-celled Pinnularia species such as P. bertrandii Krammer (2000: 122) and P. perirrorata Krammer (2000: 41) differ sufficiently in valve outline and axial area to exclude all conspecificity.