Encyonema bonapartei Heudre, C.E. Wetzel & Ector, 2016

Heudre, David, Wetzel, Carlos E. & Ector, Luc, 2016, Encyonema bonapartei sp. nov.: a new freshwater diatom species (Cymbellales, Bacillariophyceae) in canals of Great East region (France), Phytotaxa 284 (4), pp. 273-280 : 275-277

Encyonema bonapartei Heudre, C.E. Wetzel & Ector sp. nov. ( Figs 2–29 )

Light microscopy ( Figs 2–23 ): Valves clearly asymmetrical and dorsiventral, semi-elliptical to semi-elliptical-lanceolate; dorsal margin greatly convex, ventral margin slightly convex; apices rounded to slightly protracted; length 11.1–16.8 μm (13.8 ± 1.3 μm), width 4.2–5.3 μm (4.8 ± 0.3 μm), l/w ratio 2.4–3.4 (3.0 ± 0.2); axial area very narrow, central area tiny often extended on ventral side by a shorter stria or a striation interruption caused by a missing stria; raphe branches straight and sinuous, slightly bent dorsally in the median region of the valve; terminal fissures indistinct or ventrally bent; striae almost parallel with areolae indistinguishable; dorsal stria density 17–22 in 10 μm (19.0 ± 1.2 in 10 μm); ventral stria density 17–21 in 10 μm (18 ± 1.0 in 10 μm), sometimes becoming 15–16 in 10 μm toward central area; an almost isolated stria in middle of dorsal or ventral side can sometimes be present; stigmoid absent. Plastids not observed because of the use of ethanol as fixing agent.

Scanning electron microscopy ( Figs 24–29 ): Striae uniseriate composed by rounded lineolae ( Figs 24, 26 ). Raphe slightly sinuous externally, bent to the dorsal side at the centre of valve; terminal fissures hooked to the ventral margin ( Fig. 24 ). Inner raphe fissure straight, with a small central nodule making proximal raphe endings very close to each other ( Fig. 27 ). Distal raphe endings terminating in helictoglossae near the last ventral striae ( Fig. 29 ). Dorsal striae continuing toward the apex, but never present in front of distal raphe ending ( Fig. 28 ). Internally, the uniseriate areolae of each stria are arranged between the virgae ( Figs 25, 27 and 29 ). At the upper position of each areola, a pair of short stubs protrudes from the opposite positions of the lateral virgae (i.e. foricula) ( Figs 25, 27 ). 40 areolae in 10 μm on dorsal side, 50 in 10 μm on ventral side. Stigmoid absent.

Type :— FRANCE. Great East region . Sampigny: East Canal northern branch (5° 30’ 55” E 48° 49’ 33” N). Holotype on slide BR4464 , deposited in Botanic Garden Meise (Belgium).

Etymology: Dedicated to French General and Emperor Napoleon Bonaparte (1789–1821). The valve shape of this species resembles his famous bicorn campaign hat.

Ecology: The E. bonapartei ecology is difficult to estimate with certainty, because it has been found in only three artificial canals which have different water characteristics. However, we can provide a first approach based on the East Canal: it showed the largest population of E. bonapartei found so far, and its physicochemical characteristics are very stable in time. The following environmental values were measured in 2013 at the same period on the Sampigny site (type locality): water temperature: 18ºC, pH 8; electric conductivity 500 μS. cm-1; dissolved organic carbon 2.2 mg. l- 1; biochemical oxygen demand <0.5 mg. l-1; orthophosphates <0.015 μg. l-1; total phosphorus 0.02 μg. l-1. The diatom community was mainly composed of Achnanthidium minutissimum ( Kützing 1833: 578) Czarnecki (1994: 157) , A. straubianum (Lange-Bertalot in Lange-Bertalot & Metzeltin 1996: 26) Lange-Bertalot (1999: 279), Encyonopsis minuta Krammer & E. Reichardt in Krammer (1997b: 95) and E. subminuta Krammer & E. Reichardt in Krammer (1997b: 96).

Figures

FIGURES 2–23. Encyonema bonapartei LM valve views (type material from Sampigny). Scale bar = 10 μm.

FIGURES 24–29. Encyonema bonapartei SEM views (type material from Sampigny). 24. Valve in external view. 25. Valve in internal view. 26. Close up on proximal raphe endings in external view. 27. Close-up of proximal raphe endings in internal view. 28. Close-up of apex in external view. 29. Close-up of apex in internal view showing distal raphe fissure ending in helictoglossae. Scale bars = 2 μm.