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

Pinnularia australodivergens nov. sp. (Figs 160–165)

Valvae lineares marginibus paene parallelis, apicibus non-protractis, late rotundatis. Longitudo 66–110 µm, latitudo 14– 19 µm. Area axialis linearis-lanceolatae, potius lata, dilatans in aream centralem. Area centralis rhombica formans fasciam rectangularem potius parvam, maculis rotundatis in marginibus. Raphe lateralis, ramis leviter undulatis. Terminationes raphis proximales rectae. Pori centrales annicibus lateralis. Fissurae raphis distales unciformes. Striae moderate radiatae in media parte valvae, graduatim fortiter convergentes ad apices, 9–11 in 10 µm. Lineae speciosae longitudinales nullae.

Valves linear with almost parallel margins and broadly rounded, non-protracted apices. Valve dimensions (n=12): length 66–110 µm, width 14–19 µm. Axial area linear-lanceolate, rather broad, widening toward the central area. Central area rhomboid, forming a rather narrow, rectangular fascia with rounded thickenings at the margins, visible in LM. Raphe lateral, slightly undulating with straight proximal raphe endings. Central pores with lateral annexes. Distal raphe fissures bayonet -shaped. Striae moderately radiate in the middle, gradually becoming strongly convergent near the apices, 9–11 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-4257 (holotype BR), slide PLP-202 (isotype University of Antwerp, Belgium), slide ZU8/17 (isotype BRM).

Habitat:— Pinnularia australodivergens could be found in a few large lakes on the central plateau of Byers Peninsula near Limnopolar lake. The lakes are characterized by a weakly alkaline pH (7.2–7.6) and a low specific conductance (<100 µS/cm).

Etymology:— The specific epithet refers to the geographic distribution of the species (Latin: ‘ australis ’ meaning southern).

Observations:— Pinnularia australodivergens clearly belongs to the P. divergens W. Smith (1853: 57) - complex based on the valve outline, dimensions and the typical rounded thickenings in the central area. The species shows some similarity with several other species and varieties in this complex, some recently raised to species rank (Kulikivskiy et al. 2010) such as P. canadodivergens Kulikovskiy, Lange-Bert. & Metzeltin (2010: 360), P. divergens var. sublineariformis Krammer 2000: 62) and P. biconstrictoides Kulikovskiy, Lange-Bert. & Metzeltin (2010: 360). P. canadodivergens can be distinguished by its more swollen middle part, the typical markings along the axial area and the lower number of striae (8–10 vs. 9–11 in 10 µm). Pinnularia divergens var. sublineariformis is much smaller with a lower valve width (11.0– 13.5 µm vs. 14–19 µm). Finally, P. biconstrictoides has a different valve outline with clearly swollen central and terminal parts of the valve, a large, rhomboid, central area and usually larger valve dimensions.