Microcostatus edaphicus C.E. Wetzel, Noga, Ector & Stanek-Tarkowska, 2016

Stanek-Tarkowska, Jadwiga, Wetzel, Carlos E., Noga, Teresa & Ector, Luc, 2016, Study of the type material of Navicula egregia Hustedt and descriptions of two new aerial Microcostatus (Bacillariophyta) species from Central Europe, Phytotaxa 280 (2), pp. 163-172 : 167-168

Microcostatus edaphicus C.E. Wetzel, Noga, Ector & Stanek-Tarkowska , sp. nov. ( Figs 18–28 )

Valve lanceolate to rhombic-lanceolate ( Figs 18–23 ). Valve ends are blunt and slightly broadly rounded. Valve dimensions (n=10): length 9.0–10.0 μm, width 3.0–3.3 μm. Transapical striae are straight, weakly radiate, 33–35 in 10 μm ( Figs 24–28 ). Striae are composed of one transapically, internally occluded elongated areola. On the edge of the valve margin and mantle, a row of elongated pores is present around the valve as a continuation of striae ( Figs 25, 27 ). Central area broadened in transapical axis. Raphe filiform, in external view the proximal ends are slightly expanded and curved (however are straighter than in M. aerophilus ), the distal ends curved in the same direction (but opposite to proximal ends), placed in a raised sternum ( Figs 24, 25, 27 ). Sternum has the same width over the entire length and is asymmetrically concave at the center ( Figs 24, 25, 27 ), which is visible under light microscopy ( Figs 18–23 ). Conopeum is absent. In internal view, on distal ends helictoglossae are present. Striae in internal view are very similar to those in external view. Areolae structure are not visible because they are occulted by silica. A row of elongated pores is located on the valve margin; pores located on the valve apices are rounded ( Figs 26, 28 ).

Type:— GERMANY. Oldenburg, Hasbruch, Forst Delmenhorst, 53.25° N, 8.75° W, F. Hustedt, 3 May 1937 (holotype BRM! N2/80, sample E1010).

Comparison with similar species:— Microcostatus edaphicus is similar to M. egregius (Hustedt) Lange-Bertalot. These species can be distinguished under LM by the distance between proximal raphe ends, which in M. egregius are 0.7–1.2 μm and is greater (1.4–1.8 μm) in M. edaphicus .

Distribution and ecology: —The species was observed by Hustedt as Navicula egregia from samples collected from mosses over the stream in Oldenburg ( Germany), which is also under aerophytic conditions.

Associated diatom flora:— The floristic element was composed of aerophytic species such as Chamaepinnularia parsura ( Hustedt 1962: 240) C.E.Wetzel & Ector in Wetzel et al. (2013: 156), Chamaepinnularia obsoleta ( Hustedt 1942a: 69) C.E.Wetzel & Ector in Wetzel et al. (2013: 158), Mayamaea fossalis ( Krasske 1929: 354) Lange-Bertalot (1997: 72) , Navicula tenelloides Hustedt (1937: 269) and Tryblionella aerophila ( Hustedt 1942a: 70) D.G.Mann in Round et al. (1990: 677).

Figures

FIGURES 18–28. Microcostatus edaphicus. 18–23. LM photographs of type material from Hustedt Collection. 24–25, 27. SEM photographs of external valve view with characteristic clearly visible elongated pores as continuation of striae. 26, 28. Internal valve view with helictoglossae.