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

Pinnularia australoglobiceps sp. nov. (Figs 189–196)

Valvae lineares-lanceolatae ad ellipticae-lanceolatae in speciminibus minoribus marginibus clare convexis, apicibus late capitatis, semper distincte angustioribus quam media parte valvae. Longitudo 25–37 µm, latitudo 8.4–9.6 µm. Area axialis angusta, leviter dilatans in aream centralem. Area centralis formans fasciam cuneiformem latam. Raphe filiformsi, ramis leviter curvatis. Terminationes raphis proximales leviter deflexae cum poris indistinctis. Fissurae raphis distales unilateraliter flexae. Striae in media parte valvae curvatae, moderate ad fortiter radiatae, parallelae ad leviter convergentes ad apices, 13–15 in 10 µm. Striae abbreviatae nonnulae in area centrali. Lineae speciosae longitudinales nullae.

Valves linear-lanceolate to elliptic-lanceolate in smaller individuals, with clearly convex margins and broadly capitate apices, always distinctly narrower than the valve middle; in smaller specimens barely offset. Shoulders between apices and valve middle absent. Valve dimensions (n=20): length 25–37 µm, width 8.4– 9.6 µm. Axial area narrow, only slightly widened towards the central area. Central area forming a large bowtie-shaped fascia. Raphe filiform with slightly curved branches and straight to slightly deflected central endings bearing simple raphe pores. Distal raphe fissures, bent to one side. Striae in the valve middle curved, moderately to strongly radiate, becoming parallel to weakly convergent near the apices, 13–15 in 10 µm. Shortened striae sometimes present near the central area. Longitudinal lines absent.

Type:— Byers Peninsula, Livingston Island, South Shetland Islands, sample BY066, leg. B. Van de Vijver, coll. date 18/01/2009, slide no. BR-4260 (holotype BR), slide PLP-205 (isotype University of Antwerp, Belgium), slide ZU8/18 (isotype BRM).

Habitat and Distribution:— Pinnularia australoglobiceps is uncommon on Livingston Island and is mainly found in aquatic habitats. The type population was observed in a small lake near the southern beaches. The lake had an almost circumneutral pH (7.2) with a low specific conductance value (104 µ S/cm). Occasionally, the species was found on wet soil and among mosses around streams and lakes, probably dispersed by wind or water sprays.

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

Observations:— The species most similar to P. australoglobiceps are P. globiceps Gregory (1856: 10), P. iatriaensis Foged (1970: 169), P. lundii Hustedt (1954: 474) and P. bottnica. Pinnularia globiceps has a lower valve width (5.0– 7.5 µm vs 8.4–9.6 µm) with larger capitate ends, usually as wide as the valve middle or only slightly narrower (Krammer 2000). The northern hemisphere species P. iatriaensis has a linear (and not an elliptic-lanceolate) valve outline with slightly undulating (and not convex) margins and a coarser striation pattern with 11–12 (vs. 13–15) striae in 10 µm (Foged 1970, Krammer 2000). Moreover, the central area in P. iatriaensis is smaller than in P. australoglobiceps. Pinnularia lundii has typically capitate, well set-off apices, contrary to P. australoglobiceps and is usually much longer (40–60 µm vs. 25–37 µm). Pinnularia bottnica, known from the coast of northern Baltic Sea has a similar striation pattern and central area but a different valve outline with only weakly protracted and obtusely rounded valve ends. In Van de Vijver et al. (2002), valves identified as P. bottnica with similarities to P. globiceps, (see plate 102, Figs 12–15) are probably conspecific but have somewhat shorter apices. Pinnularia austroshetlandica possess a similar raphe structure and striation pattern but has narrower, shorter and clearly rostrate ends.

Carlson described the species Caloneis austrogeorgica Carlson (1913: 12) from South Georgia. Since type material has yet been located, only one drawing and a rather short description are available for comparison with P. australoglobiceps. The valve dimensions given for C. austrogeorgica are somewhat higher, especially the valve width, an important morphological character; this is almost 1/5 higher in the latter (12 µm vs. 8.4– 9.6 µm in P. australoglobiceps). Until type material has been found and investigated, both species are considered independent.