Encyonema menezesiae W.J.Silva & M.G.M.Souza, 2015

Silva, Weliton José Da & Souza, Maria Das Graças Machado De, 2015, New species of the genus Encyonema (Cymbellales, Bacillariophyta) from the Descoberto River Basin, Central-western Brazil, Phytotaxa 195 (2), pp. 154-162 : 156-157

Encyonema menezesiae W.J.Silva & M.G.M.Souza sp. nov. ( Figs 2–16 )

Type:— BRAZIL. Distrito Federal / Goiás: Descoberto River , downstream from the dam, 15º46’52”S ; 48º13’56”W, rocks, 23 June 2003, Souza (without number) [holotype: a specimen marked on slide UB 01495 in Herbarium of Universidade de Brasília ( UB) ( Fig. 2 )] .

Diagnosis: —Differs from E. gaeumannii (Meister) Krammer in outline, the density of the striae and areolae, and the shape of the foramina.

Description: —Valves dorsiventral, lanceolate, dorsal margin convex, ventral margin straight to convex; ends subcapitate to rostrate-capitate; length: 12–22 μm, breadth: 3–6 μm, length/breadth ratio: 3.0–5.6; axial area narrow, linear-lanceolate, smooth externally and internally; central area indistinct; raphe filiform; external fissures of raphe irregular, external proximal fissures of raphe slightly expanded, pore-like, and deflected to dorsal side; external terminal fissures of raphe hooked, deflected to ventral side; internal fissures of raphe straight, internal proximal fissures hooked to dorsal side, merged, forming very narrow intermissio, internal terminal fissures ending in helictoglossae slightly deflected to ventral side; striae as large as transapical costae, with deep alveoli, parallel to slightly radiate, 8–13 striae in 10 μm; areolae with linear foramina externally and internally, foramen lips inconspicuous or absent, some specimens with fused areolae close to one of the valvar ends, fused areolae are externally in triangular configuration and surrounded by external terminal fissure of raphe; 44–53 areolae in 10 μm; isolated pores absent.

Etymology:— The species is dedicated to Dr. Mariângela Menezes, from the Museu Nacional, Universidade Federal do Rio de Janeiro, who has actively contributed to the taxonomy and phylogeny of microalgae from Brazil.

Material analyzed:— UB 01495, UB 01496, UB 01497, UB 01612.

Ecology:— Encyonema menezesiae occurred in four samples, in both the dry and wet seasons, in slightly acid waters (pH: 6.37–6.54) with turbidity from 2.80 to 6.36 μT. Conductivity varied between 14.3 and 38.9 mS. cm-1, except during the wet season when E. menezesiae occurred at site 10, where the conductivity reached 163.6 mS. cm-1. Dissolved oxygen varied from 3.82 to 7.90 mg.L- 1, and COD from 5.6 to 28.9 mg.L- 1. E. menezesiae occurred in sites with low concentrations of ammonium (0.07–0.17 mg.L- 1), except during the rainy season when site 10 showed relatively high concentrations of ammonium (9.35 mg.L- 1), nitrate (0.2–0.6 mg.L- 1) and nitrite (0.001 –0.088 mg.L- 1).

Figures

FIGURES 2–16. Encyonema menezesiae sp. nov. 2–8. Valve view, LM. 9–12. External valve view, SEM. 13, 14. Ends in external valvar view, SEM, showing hooked external terminal fissure of the raphe. 15, 16. Internal valvar view in SEM. Scale bars: Figs 2–8 = 10 μm; Figs 9–12, 15, 16 = 2 μm; Figs 13, 14 = 1μm.