Microcostatus aerophilus Stanek-Tarkowska, Noga, C.E. Wetzel & Ector, 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 : 165-167

Microcostatus aerophilus Stanek-Tarkowska, Noga, C.E. Wetzel & Ector , sp. nov. ( Figs 2–17 )

Valves lanceolate to elliptical-lanceolate with broadly rounded ends ( Figs 2–12 ). Observed range of valve dimensions (n=30): length 6.3–11.6 μm, width 2.6–4.2 μm ( Figs 7–12 ). Striae strongly radiate, 40–50 in 10 μm, in the valve margin covered by wide coat of pseudoconopeum ( Figs 13–15, 17 ). Raphe straight in sternum. Raphe branch filiform. The proximal raphe ends are slightly expanded and curved in the same direction ( Figs 13, 15, 17 ). Terminal raphe endings hooked and deflected to the same side. Sternum asymmetrically constricted ( Figs 13–15 ), which is clearly visible under light microscopy ( Figs 2–12 ). The axial area includes depressions on both sides of the sternum, visible under light microscope as arch-shaped shadows ( Figs 2–12 ). The depressions contain small costae ( Fig. 13 ). Central area broadened to margins. Pseudoconopeum very wide with small external perforations but very clearly visible under SEM ( Figs 13, 15 ). Pseudoconopeum perforations extend (mostly at the valve apex) on the mantle. Cingulum is not perforated ( Fig. 16 ). Authors were not able to observe the internal valve.

Type:— POLAND. Podkarpacie Province, Husów, 49° 58’ 22.48” N, 22° 16’ 36.54” E, J. Stanek-Tarkowska, 13 July 2013 (holotype PIRCE! 20138, illustrated in Fig. 9 ).

Etymology: —The species name aerophilus refers to the typical habitat of this species.

Comparison with similar species:— Microcostatus aerophilus is morphologically very similar to M. krasskei — both have similar dimensions and number of striae in 10 μm, however, in M. krasskei pseudoconopeum is not present

( Johansen & Sray 1998). Under light microscope, the valve shape and asymmetrically constricted sternum are very similar, therefore correct identification is possible only under SEM.

Distribution and ecology:— The species was found at both sites in Husów, southeastern Poland, in every month from April to November 2013. It was observed most numerously in July at site number two (about 0.5% of relative abundance). Those sites were shaded by young deciduous trees. The soil was characterized by a slightly acid pH (5.7 in July), and the highest nitrogen and carbon content in all samples ( Table 1).

Associated diatom flora:— Together with Microcostatus aerophilus the most frequent species in the assemblage were Humidophila contenta (Grunow in Van Heurck 1885: 109) R.L. Lowe et al. (2014: 357), Pinnularia obscura Krasske (1932: 117) and Stauroneis thermicola (J.B. Petersen 1928: 394) J.W.G. Lund (1946: 61) (>25% for each other). Also found in smaller numbers were (15–25%) Hantzschia amphioxys ( Ehrenberg 1843: 413) Grunow in Cleve & Grunow (1880: 103) and Pinnularia borealis Ehrenberg (1843: 420) ( Table 1).

Comments: — Microcostatus aerophilus was also found in sample E1011 from the Hustedt Collection. In this material it occurred very rarely—valve dimensions: 8.0–12.0 μm in length, 3.0–3.3 μm in width and 44–46 striae in 10 μm ( Figs 2–6 ).

Figures

FIGURES 2–17. Microcostatus aerophilus. 2–6. LM photographs from Hustedt German material.7–12. Holotype population from Husów material. 13–15. SEM photographs in external valve view illustrating variation in size, outline and conopea with perforation. 16. External girdle view from Husów. 17. External valve view with clearly visible asymmetrical constricted sternum from Hustedt German material.