Microcostatus egregius (Hustedt) Lange-Bertalot, 1999

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 : 168-169

Microcostatus egregius (Hustedt) Lange-Bertalot ( Figs 29–56 )

Basionym: Navicula egregia Hustedt (1942a : fig. 26, here reproduced as Fig. 29 )

Valve lanceolate ( Figs 30–52 ). Observed range of valve dimensions (n = 25): length: 7.2–13.9 μm, width: 3.1–3.7 μm. Transapical striae weakly radiate and slightly arcuate, 33–35 in 10 μm ( Figs 53–56 ). Striae in central area shortened, slightly protruding or hidden under pseudoconopeum ( Figs 53, 55, 56 ). Externally on the valve margin a row of elongated striae is present, while on the valve mantle there is a row of pores as a continuation of the striae ( Figs 53, 55 ). Distal raphe ends curved in the same direction onto the mantle ( Figs 53, 55, 56 ). Raphe almost straight, in raised sternum, narrowing at the ends ( Figs 53, 55 ). Conopeum is visible in the axial area. In the place of the sternum and conopeum connection, a continuous row of perforations on each side are present ( Fig. 53 ). In some specimens (in low degree of silification), the conopeum is narrow and rolled up ( Fig. 53 ), while in other valves have wider and flat conopeum ( Figs 55, 56 ). Pseudoconopeum with row of perforation present on the valve margin ( Fig. 53 ). In internal view, the raphe is straight, proximal endings are very slightly curved in the same direction. On distal ends small helictoglossae are present ( Fig. 54 ).

Distribution and ecology:— Species noted from Germany, near Bremen, developing beyond the aquatic environment and among mosses ( Krammer & Lange-Bertalot 1986: 202). Lange-Bertalot & Steindorf (1996: 655) stated Navicula egregia as an aerophilous diatom, occurring very rarely in Germany (R category). Ettl & Gärtner (1995: 70) concluded that it is an aerophytic species, developing on mosses and in wet places in Germany and Finland. Navicula egregia was recorded from lakes and ponds in the Canadian High Arctic Archipelago, where it occurred in alkaline pH (8.3–8.5) and moderate conductivity (˃240 μS/cm) ( Antoniades et al. 2005: 36, 2014: 617). Similar specimens were observed on the North American continent and named as cf. Microcostatus egregius ( Antoniades et al. 2008: 164) or Microcostatus cf. egregius (Silver & Hamilton 2011: 197) .

Figures

FIGURES 29–56. Microcostatus egregius. 29. Drawing of Navicula egregia Hustedt 1942a. 30–52. LM photographs of Hustedt type material. 53, 55–56. SEM photographs of external valve view illustrating a row of perforation in the place of sternum and conopeum connection. 54. Internal valve view with helictoglossae.