Luticola evkae Kopalova 2011, sp. nov.

Luticola evkae Kopalová, sp. nov. (Figs 35–50)

Valvae ellipticae-lanceolatae marginibus clare convexis apicibusque capitatis, late rotundatis. Valvae minores paene ellipticae. Longitudo 14–22 µm, latitudo 5.4–8.2 µm. Area axialis latissima, lanceolata, leviter dilata in aream centralem. Ad apices, area axialis clare dilata. Area centralis formans staurum paene rectangularem, leviter dilatatum ad margines, marginatumque serie una areolarum minutissimarum. Stigma rotundata, punctiformis solitaria adest inter mediam partem valvae marginesque. Raphe filiformis, recta terminationibus proximalibus unilateraliter deflexis opposita stigma poris centralibus leviter expansis. Fissurae distales curtae, leviter deflexis. Striae transapicales radiatae in parte centrali valvae ad fortiter radiatae ad apices, 16–20 in 10 µm. Areolae rotundae 1–2 per striam terminans in areolam transapicaliter elongatam ad marginem.

Type:— ANTARCTICA. James Ross Island, Ulu Peninsula, Vondra II Lake, sample D39, leg. L. Nedbalová, coll. date 19/01/2009, slide no. BR-4242 (holotype BR, Fig. 46 is the encircled holotype specimen), slide PLP-190 (isotype University of Antwerp, Belgium), BRM-ZU8/08 (isotype BRM).

Valves elliptic-lanceolate with clearly convex margins and broadly rounded, capitate apices (Figs 35–46). Smaller valves almost elliptical (Fig. 47). Valve length 14–22 µm, valve width 5,4–8,2 µm (n=32). Axial area very broad, lanceolate, slightly widening towards central area (Fig. 48). Towards apices, axial area clearly widened (Fig. 49). Central area forming almost rectangular stauros, slightly widening towards margins, bordered by one series of very small rounded areolae (Fig. 50). One small, solitary, rounded stigma present, halfway between valve centre and margin (Figs 48, 50). Raphe branches filiform, straight with unilaterally deflected proximal endings away from stigma, terminating in weakly expanded central pores (Figs 48, 50). Distal fissures short, slightly deflected (Fig. 49). Transapical striae radiate near valve centre to strongly radiate towards poles, 16–20 in 10 µm, composed of two (occasionally 1) small rounded areolae terminating in one clearly transapically elongated areola in middle part of valve near margin (Fig. 50). Areolae always rounded near apices (Fig. 49). Internal structure not observed.

Habitat, Ecology and Distribution:— Luticola evkae was described from the epilithon of a small, stable, shallow lake on Lagoons Mesa in the ice-free area close to Croft Bay. The lake had a pH of 7.7, a low specific conductance of 53 µS/cm and was dominated by several Nitzschia species such as Nitzschia perminuta, Nitzschia paleacea Grunow (in Van Heurck 1881: pl. 68, Figs 9–10) and Nitzschia gracilis Hantzsch (1860:40).

Etymology:—Named after my dear friend, Eva (Evka) Volemanová (Prague, Czech Republic).

Observations: — Based on valve dimensions and the shape of the axial and central area of the valves, Luticola evkae may at first appear similar to Luticola dolia and L. doliiformis. These three species can, however, be clearly distinguished based on their contrasting valve outlines. Luticola evkae has a typical elliptical central part of the valve whereas both L. doliiformis and L. dolia always have more elongated valves with, in most cases, almost parallel margins (Esposito et al. 2008). The apices in L. evkae are always broader and more capitate than in L. dolia, which has more rostrate to weakly capitate apices. This can be appreciated by the differences in valve width/apex ratio, which is 1.70±0.18 (n=13) in L. evkae and 2.36±0.22 (n=13) in L. dolia; L. doliiformis has wider apices. Additionally, the shoulders just below the apices are more oblique in both L. dolia and L. doliiformis. In L. evkae, the outer row of areolae is always composed of transapically elongated areolae clearly visible in LM, whereas in L. doliiformis these areolae are always strictly rounded. Luticola austroatlantica is similar but distinguished by a different striation pattern with larger, usually elongated areolae. Moreover, L. austroatlantica lacks the broad axial area and has a more elongated valve outline. Smaller valves of L. austroatlantica with comparable valve dimensions as L. evkae always have rostrate apices contrary to the capitate apices in L. evkae. Other species that might be considered morphologically similar include L. muticopsis (and its smaller forms) and L. palearctica (Hustedt 1966: 613) D.G.Mann (in Round et al. 1990: 671). The former has a different valve outline, with one straight and one convex margin, clearly deflected proximal and distal raphe endings, rostrate apices and a narrower axial area (Van de Vijver & Mataloni 2008), whereas the latter is larger with more expanded apices and a higher areola density (Hustedt 1966). Finally, L. truncata has more areolae per stria (3–4 vs. 1–2 in L. evkae) with a more elliptical outline and truncated, non-capitate apices (Kopalová et al. 2009).