Luticola tomsui Kopalova 2011, sp. nov.

Luticola tomsui Kopalová, sp. nov. (Figs 73–87)

Valvae lineares ad lineares-ellipticae apicibus late rotundatis. Margines clare sed asymmetrice constrictae in media parte valvae. Longitudo 18.5–23 µm, latitudo 6.5–8.1 µm. Area axialis lata, lanceolata, clare dilatata ad apices areamque centralem. Area centralis formans staurum rectangularem ad paene ellipticum, marginatum serie una areolarum parvarum rotundatarum ad leviter transapicaliter elongatarum. Stigma rimiformis solitaria adest, inter mediam partem valvae marginesque. Raphe filiformis, terminationibus proximalibus recta unilateraliter deflexis opposite stigma poris centralibus indistinctis. Fissurae distales curtae, leviter deflexae. Striae transapicales radiatae omnino, positae prope margines valvae, 16–18 in 10 µm. Areolae 1–2 rimiformes. Ad margines, areola expansa adest.

Type:— ANTARCTICA. James Ross Island, Ulu Peninsula, Vondra II Lake, sample D39, leg. L. Nedbalova, coll. date 19/01/2009, slide no. BR-4244 (holotype BR, Fig. 78 is the encircled holotype specimen), slide PLP-192 (isotype University of Antwerp, Belgium), BRM-ZU8/10 (isotype BRM).

Valves linear to linear-elliptic with broadly rounded, capitate apices (Figs 73–83). Stigma-bearing side almost straight with opposite side more convex. Valve margins clearly convex but asymmetrically constricted near valve middle. Valve length 18.5–23 µm, valve width 6.5–8.1 µm (n=15). Axial area broad, lanceolate, widening towards apices and central area, (Fig. 84). Central area forming rectangular to almost elliptical stauros, bordered by one series of small rounded to very weakly transapically elongated areolae (Figs 84, 85). One small slit-like solitary stigma present, halfway between valve centre and margin (Fig. 85). External raphe branches straight to weakly curved with unilaterally deflected proximal raphe endings, away from the stigma, terminating in almost unexpanded central pores (Fig. 85). Distal raphe fissures short, weakly deflected (Fig. 86). Transapical striae radiate throughout entire valve, positioned close to valve margin, 16–18 in 10 µm (Fig. 84). Striae composed of 1–2 small, slitlike areolae and one enlarged areola close to valve margin (Fig. 84). Towards apices, striae composed only one areola. Internally, poroids of valve face occluded by hymens, forming continuous strip on each stria. Internal stigma opening consisting of small, rounded lipped slit. Stauros clearly developed (Fig. 87). Internal proximal raphe endings straight, terminating on stauros edge. Distal raphe endings terminating on small helictoglossae (Fig. 87).

Habitat, Ecology and Distribution:— Luticola tomsui has been found in only two samples from one lake on James Ross Island. The largest population was found in the epilithon of the shallow Vondra II Lake located on the Lagoons Mesa plateau near the ice-free area close to Croft Bay. The lake had a pH of 7.7, a low specific conductance value (53µS/cm) and was dominated by Nitzschia species including Nitzschia perminuta, N. paleacea and Nitzschia gracilis.

Etymology:— Luticola tomsui is named after my dear friend Jan Tomš ů (Prague, Czech Republic).

Observations: — The number of Luticola taxa with constricted valves is low thus confusion with L. tomsui is unlikely. Recently, L. adelae was described from White Lake on James Ross Island (Van de Vijver et al. 2011) and L. binodis (Hustedt 1922: 239) Edlund (in Edlund et al. 2001: 85) was reported from the nearby Livingston Island (South Shetland Islands) (Van de Vijver et al. 2011). Both are species with constricted valves. The valve size ranges of L. tomsui (L 18–23 µm, W 6,5 –8.0 µm) is in between those of L. adelae and and L. binodis: L. adelae is smaller (L 16–20 µm, W 5–6 µm), L. binodis is larger (L ± 24 µm, W ± 7,5 µm). L. adelae and L. binodis both differ from L. tomsui in having a more slender valve outline and less inflated valve centre. Additionally, the number of areolae per stria in L. binodis is higher than L. tomsui and the axial area is smaller compared to the rather broad axial area in L. tomsui.

Other species with constricted valves, such as L. mollis Lange-Bertalot & Rumrich (in Rumrich et al. 2000: 149) and L. incoacta (Hustedt 1966: 619) D.G.Mann (in Round et al. 1990: 670), have a higher number of areolae per stria, a narrower axial area and deeper constrictions.

Finally, when L. tomsui is compared to L. nivalis, the latter has a valve outline with more undulations.