Staurosirella pulchella Levkov & D.M.Williams, 2011

Levkov, Zlatko & Williams, David M., 2011, Fifteen new diatom (Bacillariophyta) species from Lake Ohrid, Macedonia, Phytotaxa 30, pp. 1-41 : 4-5

Staurosirella pulchella Levkov & D.M.Williams , sp. nov. ( Figs 10–17 , 40, 41 )

Synonym:— Fragilaria pinnata Ehrenberg sensu Jurilj 1954 , partim fig. 12i

Valvae isopolares, lineares ad lineares–lanceolatae apicibus anguste rotundatis. Longitudo valvae 19–43 µm, latitudo valvae 7–10.5 µm. Area axialis late lanceolatae, ad apices gradatim atenuata. Striae transapicales crassae, distante positae inter se 4.5–5.5 in 10 µm, paralella е in media parte, radi а ntes ad apices.

Type:— MACEDONIA: Lake Ohrid, Biological station , transect, sand 34 m depth, collection date: 3 April 2007 (Accession No. MKNDC 001234 ). Slide BM 101467 (holotype). Slide MKNDC 001234 (isotype) .

Valves isopolar, linear to linear–lanceolate with narrowly rounded ends. Valve length 19–43 µm, valve width 7.0– 10.5 µm. Axial area broad–lanceolate, tapering towards the valve ends. Striae coarse, distantly spaced, 4.5–5.5 in 10 µm, parallel in the middle, becoming radiate towards the valve ends (LM).

Externally, valve striae with robust virgae joining large central sternum; vimines thin, parallel, appear unoccluded; striae raised above surface ( Figs 40, 41 ). Virgae at mantle junction with spines, 2–4, not well pronounced ( Figs 40, 41 ). Apical pores fields probably at each pole, set off from valve features, almost as ocellulimbus ( Fig. 41 ). Girdle unknown ( SEM).

Distribution and ecology:— Staurosirella pulchella was observed in the sediment of Lake Ohrid at depths from 20– 35 m. According to Jurilj (1954), S. pulchella was observed in the zone inhabited by Chara spp. (10–15 m depth), again in the sediment (mud). So far, there are few records of this species in Lake Ohrid; it was not found in Lake Prespa ( Levkov et al. 2007).

Observations: — Staurosirella pulchella is comparable to several Staurosirella ( Fragilaria sensu lato) taxa. Fragilaria clevei Pantocsek (1902 : figs 9: 216, 217) has similar valve outline, but it differs from S. pulchella in respect of shape of the axial area (narrow, linear in F. clevei ) and striae density (6–7 in 10 µm). Hustedt (1931: 161) synonymized F. clevei with F. pinnata var. intercedens (Grunow) Hustedt [= F. mutabilis var. intercedens Grunow in Van Heurck (1880: fig. 45: 13 = Staurosirella pinnata var. intercedens (Grunow) Hamilton ]. Fragilaria pinnata var. intercedens is characterized by linear valves with parallel sides and narrow, linear axial area. Fragilaria mutabilis var. robusta Skvortzow & Meyer (1928 : fig. 1: 8) was treated as a synonym of F. pinnata var. intercedens ( Hustedt 1931: 161) . However, F. mutabilis var. robusta has broadly lanceolate and much wider valves (B= 13.6 µm), opposite to linear, symmetrical valves in F. mutabilis var. intercedens . On the other hand F. mutabilis var. baicalensis Skvortzow & Meyer (1928 : fig. 1: 9) has asymmetrical to oval and smaller valves (L= 25.5–28.0 µm) with very narrow, linear axial area. Staurosirella lapponica (Grunow) Williams & Round (1987 : fig. 21, 26, 27) (= F. lapponica Grunow ) is characterized by linear valves with parallel sides 12–40 µm long and 4–6 µm wide. Staurosirella leptostauron var. dubia (Grunow) Edlund (1994 : fig. 31) (= F. harrisoni var. dubia Grunow ) has elliptic-lanceolate valves with broadly lanceolate axial area, and 6–7 striae in 10 µm, opposite to linear-lanceolate valves with linear to narrow lanceolate axial area and 4–5 striae in S. pulchella .

Figures

FIGURES 1–24. LM micrographs. Figs 1–9. Odontidium minutum. Figs 10–17. Staurosirella pulchella. Figs 18–24. Navicula subviridula. Scale bar = 10 µm.

FIGURES 40–45: SEM micrographs of Staurosirella pulchella and S. lata. Figs 40, 41. Staurosirella puchella. Fig. 40. SEM external valve view. Fig. 41. Detail of the valve apex showing the striae structure and APF. Figs 42–45. Staurosirella lata. Figs 42, 44. external view of frustule and girdle bands. Fig. 43. Detail of valve apex showing the striae structure and APF. Fig. 45. Internal view of valve apex showing areolae occlusions and APF. Scale bars in Figs 40, 42, 45 = 5 µm, Fig. 44 = 10 µm; Figs 41, 43 = 2 µm.