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

Pinnularia subaltiplanensis sp. nov. (Figs 29–35)

Valvae lineares ad angustissime lanceolatae, marginibus parallelis ad leviter convexis. Apices in speciminibus maioribus leviter protractae, late subrostratis, in speciminibus minorobus late rotundatae. Longitudo 21–28 µm, latitudo 3.6– 4.5 µm. Area axialis angusta, linearis, non dilatans in aream centralem. Area centralis formans fasciam latam, aliquando asymmetricam. Raphe filiformis, ramis rectis, terminationibus raphis proximalibus unilateraliter leviter deflexis cum, extensis in aream centralem. Terminationes raphis distales paene non discernandae in LM, falcatae. Striae leviter ad moderate radiatae in media parte valvae, convergentes ad apices, 16–19 in 10 µm. Lineae speciosae longitudinales nullae.

Valves linear to narrowly lanceolate with parallel to slightly convex margins. Apices in larger specimens slightly protracted and broadly subrostrate, in smaller valves clearly broadly rounded. Valve dimensions (n=10): length 21–28 µm, width 3.6–4.5 µm. Axial area narrow, linear, almost not slightly widened towards the valve middle. Central area forming a large, occasionally asymmetrical, fascia, about ¼ to ⅓ of the valve length. Raphe straight with weakly deflected proximal endings, extending well beyond the last central striae, terminating in clearly expanded central pores, moderately distantly spaced. Distal raphe fissures barely visible, probably sickle-shaped. Striae weakly to moderately radiate near the centre, convergent at the apices, 16–19 in 10 µm. Longitudinal lines not visible in LM.

Type:— Hurd Peninsula, Livingston Island, South Shetland Islands, sample A24/2006, leg. R. Zidarova, coll. date 27/12/2005, slide no. BR-4261 (holotype BR), slide PLP-206 (isotype University of Antwerp, Belgium), slide ZU8/27 (isotype BRM).

Habitat:— The largest population of P. subaltiplanensis was observed on Hurd Peninsula where the species was found in low abundances in a small brook flowing out from a shallow lake with a low specific conductance (58 µS/cm) value and pH of 6.3. Occasionally the species was found in a wet moss vegetation growing around small puddles. On Byers Peninsula, only a few valves were observed.

Etymology: —The specific epithet refers to its close resemblance to P. altiplanensis Lange-Bert., Krammer & Rumrich in Rumrich, Lange-Bert., & Rumrich 2000: 197).

Observations:— Pinnularia subaltiplanensis is most similar to P. altiplanensis but the valves are narrower than the type population of P. altiplanensis from the Chilean Altiplano (3.6–4.5 vs. 4–6 µm in P. altiplanensis) giving them a more slender outlook. The central raphe endings in P. subaltiplanensis are more distantly spaced than in P. altiplanensis. Pinnularia laucensis is smaller, with a maximum length of up to 20 µm and a valve width of 3.3–4.5 µm compared to 21–28 µm and 3.6–4.5 µm in subaltiplanensis, and has less radiate, widely spaced striae (11–14 vs. 16–19 in 10 µm). Other similar species are P. schoenfelderi, P. frauenbergiana Reichardt (1985: 182) and P. kuetzingii Krammer (1992: 104), all known from Europe (Krammer 2000). Pinnularia schoenfelderi can be easily separated based on the larger valve width (5–7 µm vs 3.6–4.5 µm) and lower stria density (13–16 vs 16–19 in 10 µm), as well as the smaller central area, less distantly spaced central raphe endings and a more lanceolate valve outline. Pinnularia frauenbergiana has comparable valve dimensions but a more elliptic-lanceolate valve outline and more densely spaced striae (18– 22 in 10 µm). Pinnularia kuetzingii differs by having a higher stria density of 18–20 in 10 µm (vs. 16–19 in 10 µm) and less distantly spaced proximal pores. Finally, P. bertrandii, according to Rumrich et al. (2000) is similar to P. altiplanensis, has broad subcapitate valve ends and an axial area that is clearly widens towards the central area (Krammer 2000).