Luticola permuticopsis Kopalova & Van de Vijver 2011, sp. nov.

Luticola permuticopsis Kopalová & Van de Vijver, sp. nov. (Figs 51–72)

Valvae lineares-lanceolatae ad lineares-ellipticae marginibus distincte convexis apicibusque late rotundatis, stricte capitatis. Longitudo 18.5–26.0 µm, latitudo 7.3–9.2 µm. Area axialis moderate angusta, linearis, paene non dilatata in aream centralem apicesque. Area centralis formans staurum rectangularem ad cuneatum, marginatum serie una areolarum rotundatarum magnarum. Stigma paene rotundata adest in extremo striae curate vel isolata inter mediam partem valvae marginesque. Raphe filiformis, recta, terminationibus proximalibus unilateraliter clare deflexis, poris centralibus leviter expansis. Fissurae distales deflectis, clare expansae. Striae transapicales fortiter radiatae omnino, 18–22 in 10 µm. Areolae 3–6 per striam, moderate magnae.

Type:— ANTARCTICA. James Ross Island, Ulu Peninsula, Vondra IV Lake, sample D44, leg. L. Nedbalova, coll. date 19/01/2009, slide no. BR-4243 (holotype BR, Fig. 55 is the encircled holotype specimen), slide PLP-191 (isotype University of Antwerp, Belgium), BRM-ZU8/09 (isotype BRM).

Valves linear-lanceolate to linear-elliptic with distinctly convex margins and broadly rounded, distinctly capitate apices (Figs 51–66). Valve length 18.5–26.0 µ m, valve width 7.3–9.2 µ m (n=15). Axial area moderately narrow, linear (Figs 67, 68), almost not widening towards apices (Fig. 72) and central area (Fig. 71). Central area forming a rectangular to wedge-shaped stauros, bordered by one series of large, rounded areolae. One solitary, almost rounded stigma present, usually at end of shortened stria, composed of 3 small, rounded areolae (Fig. 67) or isolated halfway between valve centre and margin (Fig. 71). External raphe branches straight with unilaterally clearly deflected, slightly expanded proximal raphe endings. Distal raphe fissures clearly elongated, deflected. Transapical striae rather strongly radiate throughout entire valve, composes of 3–6 moderately large, rounded areolae, 18–22 in 10 µm. Near central area, areolae close to margin, clearly enlarged (Figs 67, 71) Internally, poroids of valve face occluded by hymens forming continuous strip on each stria (Fig. 69). Internal stigma opening consisting of almost rounded lipped slit (Fig. 70). Stauros clearly developed (Fig. 70). Internal proximal raphe endings straight, terminating on edge of stauros. Distal raphe endings terminating on small helictoglossae (Fig. 69).

Habitat, Ecology and Distribution:— Luticola permuticopsis has been found in a few lakes on James Ross Island on the Lagoons Mesa plateau near the ice-free area close to Croft Bay. The largest population was found in the epilithon of a perennial shallow lake with a pH of 7.4, a specific conductance value of 60 µS/cm and a temperature 6.8 °C. Dominant species in the sample include Nitzschia gracilis, N. paleacea and N. perminuta.

Etymology: — permuticopsis refers to the close resemblance to L. muticopsis (per -: Latin for ‘quite equally’).

Observations: — The past few years, a large number of capitate species of Luticola have been separated from Luticola muticopsis s.l. Table 1 includes the main morphological characters of these species, in comparison to L. permuticopsis. Luticola permuticopsis can be separated from L. muticopsis by its typical valve outline: L. muticopsis has one straight and one convex margin, L. permuticopsis always has two convex margins; the apices in L. muticopsis are always more rostrate than capitate, contrary to L. permuticopsis, which has capitate, broadly rounded apices. Another important difference is formed by the areola pattern: in L. permuticopsis the striae are composed of 3–6 moderately large, densely packed areolae, whereas in L. muticopsis, there are only 3–4, more spaced areolae present, a feature easily discernible in LM (Van de Vijver & Mataloni 2008: p. 463, Fig. 77). Finally, the proximal raphe endings in L. permuticopsis are deflected, whereas in L. muticopsis, they are clearly bent. These differences separate the two species.

*measurements based on line drawing in original publication

Carlson (1913) described Navicula muticopsis f. capitata while Peragallo (1921) described Navicula muticopsis var. capitata —both separated by their asymmetrical valve outline, with one straight and one convex margin. Both taxa have a strong affinity with L. muticopsis but type material of neither can be investigated due to lack of material.

Other similar species are L. austroatlantica, L. palearctica, L. dolia and L. murrayi (West West 1911: 285) D.G.Mann (in Round et al. 1990: 671) sensu Hustedt (1966). Luticola austroatlantica can be separated by its more slender, elongated valve outline and a lower number of areolae per stria [2–3(4) vs. 3–6 in L. permuticopsis] (Esposito et al. 2008). Luticola permuticopsis has a more compact, robust outline. Moreover, near the apices, the areolae in L. permuticopsis continue almost entirely to the end, whereas in L. austroatlantica there is a hyaline zone surrounding the apices. Finally, the distal raphe fissures in L. austroatlantica are shorter than in L. permuticopsis.

Luticola palearctica has similar valve dimensions to L. permuticopsis (Hustedt 1966) but a more clearly elliptical valve outline and broadly rounded, large capitate apices, showing little difference between the width of the apices and the width near the central area. In L. permuticopsis the apices are always clearly more narrower than the valve centre. Its discrimination from Luticola murrayi sensu Hustedt (1966) is based on valve outline, with L. murrayi sensu Hustedt (1966) having broadly rounded margins and apices. The latter is currently under revision and will be described as a new species separate from L. murrayi s.s. (Van de Vijver et al., unpubl.).

Finally, L. dolia has straighter valve margins and a large axial area with only 1–3 areolae per stria (Esposito et al. 2008 and this paper). It can be separated from two other species present on James Ross Island: Luticola gigamuticopsis is much larger (length 38–46 µm, width 14–17 µm vs. 8.5–23.0 µm and 6.5–8.1 µm in L. permuticopsis) (Van de Vijver & Mataloni 2008); Luticola gaussii has an almost elliptical valve outline with constricted broadly rounded, large apices.