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

Pinnularia australoschoenfelderi sp. nov. (Figs 48–74)

Valvae lineares ad lineares-lanceolatae, marginibus parallellis ad leviter convexis in media parte valvae, graduatim decrescentibus in apices non-protractos, anguste rotundatos. Longitudo 25–38 µm, latitudo 4.6–6.0 µm. Area axialis angusta, linearis, aliquando dilatans in aream centralem. Area centralis formans fasciam latam, cuneiformem ad rectangularem. Raphe filiformis, ramis leviter curvatis. Terminationes raphis proximales extensae ultra strias centrales, deflexae cum poris parvis expansis. Fissurae raphis distales paene non discernandae in LM,similes signo interrogationis. Striae radiatae in media parte valvae, convergentes ad apices, 10–12 in 10 µm. Lineae speciosae longitudinales nullae.

Valves linear to linear-lanceolate with parallel to weakly convex margins, gradually narrowing towards the non-protracted, narrowly rounded apices. Valve dimensions (n=25): length 25–38 µm, width 4.6–6.0 µm. Axial area narrow, linear, occasionally widening towards the central area. Central area forming a large, bowtie-shaped to rectangular fascia. Raphe filiform with weakly curved raphe branches. Proximal raphe endings extending well beyond the last central striae, deflected and terminating in small, expanded raphe pores. Distal raphe fissures difficult to resolve in LM,?-shaped. Striae radiate near the valve middle, becoming convergent towards the apices, 10–12 in 10 µm. Longitudinal lines absent.

Type:— Byers Peninsula, Livingston Island, South Shetland Islands, sample BY068, leg. B. Van de Vijver, coll. date 18/01/2009, slide no. BR-4253 (holotype BR), slide PLP-198 (isotype University of Antwerp, Belgium), slide ZU8/20 (isotype BRM).

Habitat:— The type population of Pinnularia australoschoenfelderi was sampled from the sandy bottom of a small pool near the southern beaches on Byers Peninsula, with an almost circumneutral pH (7.2) and a low specific conductance (<100 µS/cm) value. The species was also found on Hurd Peninsula, usually rare but more abundant in soil under wet moss vegetations and among wet mosses surrounding shallow pools.

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

Observations:— Pinnularia australoschoenfelderi can be confused with P. schoenfelderi; the latter differs in having a higher stria density (13–16 in 10 µm vs. 10–12 in 10 µm) giving the species a finer striation pattern. Pinnularia frauenbergiana has even more striae per 10 µm (18–22 vs. 10–12 in 10 µm). Pinnularia obscura has a more irregular striation pattern with a clear shift in stria direction halfway between the central area and apices. Pinnularia obscuriformis Krammer (2000: 51) has comparable dimensions but more linear valves with acutely rounded apices.