Staurosirella lata Levkov, D.M.Williams & Cvetkoska, 2011

Levkov, Zlatko & Williams, David M., 2011, Fifteen new diatom (Bacillariophyta) species from Lake Ohrid, Macedonia, Phytotaxa 30, pp. 1-41 : 5-8

Staurosirella lata Levkov, D.M.Williams & Cvetkoska , sp. nov. ( Figs 31–39 ; 42–45 )

Synonym:— Staurosirella leptostauron (Ehrenberg) D.M.Williams & Round sensu Levkov et al. 2007 : fig. 19: 26

Cellulae solitariae. Frustula aspectu cinguli rectangulata. Valvae late tumidae in media parte cruciateformis interdum minime asymmetricae. Apices valvarum late rotundatae. Longitudo valvae 35–45 µm, latitudo valvae 26–30 µm. Area axialis late lanceolatae, attenuata versus apices. Striae transapicales crassae, radiantes, 4–5 in 10 µm.

Type:— MACEDONIA: Lake Ohrid, St. Naum springs, sublacustrine spring, mud, 1.5 m depth, collection date: 26 September 2002. Accession No. MKNDC 000132 . Slide BM 101468 (holotype). Slide MKNDC 000254. (isotype).

Cells solitary, frustule rectangular in girdle view. Valves strongly swollen at middle, cruciform, occasionally asymmetrical. Valve ends broadly rounded. Valve length 35–45 µm; valve width 26–30 µm. Axial area broad and distinct, tapering towards poles. Striae coarse, radiate, 4–5 in 10 µm (LM).

Valves cruciform, occasionally asymmetrical ( Figs 42–44 ). Valve poles broadly rounded ( Figs 42–45 ). Sternum broad, distinct, tapering towards poles ( Figs 42, 43, 45 ). Externally, valve striae with robust virgae joining large central sternum; vimines thin, parallel, appear un-occluded; striae raised above surface ( Figs 42– 45 ). Only very faint indication of spines at mantle junction, mostly at poles ( Fig. 43 ). Apical pores fields probably at each pole, but differing: one pole with narrow, parallel columns ( Fig. 45 ), the alternate pole almost invisible ( Figs 43–44 ). Few bands, valvocopula open, large, copulae open; bands diminish in size away from valve ( Fig. 44 ) ( SEM).

Distribution and ecology:— Staurosirella lata was frequently observed in the epipsammic communities near the sublacustrine springs in St. Naum. These sublacustrine springs are calcareous–rich and appear as white unstable (bubbling) plaques “inserted” in dark brown organic sediment. Here the diatom community is dominated by Cocconeis pseudothumensis Reichardt (1982 : figs. 1: 1–5) and C. neothumensis Krammer (1990: figs 21–39), while S. lata is usually rare. So far it has only been found in such habitats in St. Naum springs—it has not been observed in the sediment (organic or inorganic) of Lake Ohrid.

Observations: — Staurosirella lata resembles S. leptostauron (Ehrenberg) Williams & Round (1987) , which is characterized with strongly inflated valves at the centre, and valve dimensions as 15–30 µm long and 10–16 µm wide, and 6–11 striae in 10 µm. The main differential character between S. leptostauron and S. lata is the valve size (L= 35–45 µm; B= 26–30 in the latter) and striae density (4–5 in 10 µm in the latter).

Odontidium harrisonii Roper appears similar to Staurosirella lata , the former now being known as a synonym of F. leptostauron , a proposal made by Hustedt (1931: 154). Hustedt’s view was followed by later authors (e.g. Patrick & Reimer 1966, Krammer & Lange-Bertalot 1991). However, the illustration of O. harrisonii in Krammer & Lange-Bertalot (1991: fig. 133: 35) is from the type material (Hull, England) and has several differences in valve size and striae density when compared to S. leptostauron . Odontidium harrisonii has a more rhombic outline, smaller and narrower valves (L= 28 µm; B= 20 µm) with 6–7 striae in 10 µm.

Staurosira harrisonii var. fossilis Pantocsek (1892 : fig. 5: 77) has smaller valves (L= 17.5 µm; B= 6.5 µm) with lanceolate shape, that are slightly inflated in the middle. Fragilaria harrisonii var. major Héribaud (1903 : fig. 10: 12) has a similar valve size (L= 35–40 µm) to S. lata ; however, differences can be observed in the valve shape (being wider at the valve ends and having a wider inflation in the mid-valve) and arrangement of the central striae. Fragilaria harrisonii var. sinuata Hustedt (1927a : fig. 7: 19), which possesses coarsely punctate, uniseriate striae, is clearly distinguished from S. lata .

Genus Fragilaria Lyngbye (1819)

Figures

FIGURES 31–39: LM micrographs of Staurosirella lata (type material). 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.