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

Pinnularia sergiplaiana sp. nov. (Figs 166–173)

Valvae lanceolatae ellipticae-lanceolatae marginibus convexis, apicibus graduatim decrescentibus, aliquando leviter protractis, late rotundatis. Longitudo 50–65 µm, latitudo 10–13 µm. Area axialis moderate lata, lanceolata, graduatim dilatans in aream centralem. Area centralis rhombica formans fasciam cuneiformem moderate latam, maculis rotundatis in marginibus. Raphe lateralis, ramis clare undulatis. Terminationes raphis proximales rectae ad leviter deflexae. Pori centrales annicibus lateralis. Fissurae raphis distales unciformes. Striae fortiter radiatae in media parte valvae, distincte convergentes ad apices, 10–12 in 10 µm. Lineae speciosae longitudinales nullae.

Valves lanceolate to elliptic-lanceolate with convex margins and broadly rounded, gradually narrowing, sometimes slightly protracted apices. Valve dimensions (n=10): 50–65 µm, width 10–13 µm. Axial area moderately large, lanceolate, gradually widening towards the central area. Central area rhomboid, forming a bowtie-shaped moderately large fascia with rounded thickenings at the margin. Raphe lateral, clearly undulating with straight to weakly deflected proximal raphe endings. Raphe pores with lateral annexes. Distal fissures bajonet-shaped. Striae strongly radiate near the valve centre, becoming distinctly convergent towards the apices, 10–12 in 10 µm. Longitudinal lines absent.

Type:— Byers Peninsula, Livingston Island, South Shetland Islands, sample BY047, leg. B. Van de Vijver, coll. date 14/01/2009, slide no. BR-4258 (holotype BR), slide PLP-203 (isotype University of Antwerp, Belgium), slide ZU8/26 (isotype BRM).

Habitat:— Pinnularia sergiplaiana could be found in several large lakes on the central plateau of Byers Peninsula near Limnopolar lake. The type population was sampled from the sediment of a large lake, characterized by a weakly alkaline pH (7.4) and a low specific conductance (108 µS/cm). So far, the species has been rarely found on Hurd Peninsula where from it was previously reported as P. media (Krammer 2000: 61) Kulikovskiy, Lange-Bert. & Metzeltin (2010: 359) (Zidarova 2008, p. 30, fig. 24).

Etymology: –The species is named in honor of our colleague Sergi Pla (Madrid, Spain), in recognition of his contribution to the knowledge of Antarctic algae.

Observations:— This new species clearly belongs to the complex of taxa around P. divergens, based on the presence of the typical rounded thickenings in the central area and the lateral annexes to the proximal raphe pores. Most of the species and varieties belonging to this complex are usually larger (Krammer 2000). Pinnularia divergens has a valve width of 14–19 µm (vs. 10–13 µm) and has clearly capitate to subcapitate apices. Pinnularia media has similar valve dimensions but is characterized by clearly capitate apices and lacks the typical fascia. Pinnularia livingstonensis sp. nov. (see below) can be distinguished by its typical parallel margins and its broadly rounded apices. Pinnularia crozetii lacks the rounded thickenings in the central area and has a more lanceolate valve outline. Pinnularia divergentissima (Kütz.1844: 93) Rabenh. (1864: 222) has a somewhat similar valve outline but lacks the central thickenings.