Encyonopsis palmeti Gassiole & Le Cohu, 2014

Cohu, René Le, Gassiole, Gilles & Coste, Michel, 2014, Three new species of Cymbellales (Bacillariophyceae) from Réunion Island, Phytotaxa 156 (3), pp. 117-132 : 126-127

Encyonopsis palmeti Gassiole & Le Cohu sp. nov.

Figures 54–72 , Figs 54–63 are of the holotype.

Valves lanceolate, weakly dorsiventral; apices shortly rostrate and broadly rounded. Length: 15.4–24.2 µm; breadth: 4–5.2 µm; maximum length/breadth ratio: 5.1. Axial area narrow and linear. Raphe filiform curved to the ventral side with proximal endings deflected to the dorsal side. Striae parallel at the center becoming weakly radiate towards the poles, 22–26 in 10 µm. SEM. Externally, proximal raphe endings slightly enlarged and bent towards the dorsal side; terminal raphe fissures curved to the ventral side and terminating close to the poles in drop-like endings. Internally, extremely short intermissio, 40–45 areolae in 10 µm.

Holotype: PC0143224 . Laboratoire de Cryptogamie. Muséum d'Histoire Naturelle. Paris.

Isotype: BR–4279 . Jardin Botanique National de Belgique. Département Bryophyta et Thallophyta. Domaine de Bouchout. Meise. Belgique.

Type locality: Ravine de l'Etang à Grand Etang . (Longitude: 55°37'52.0"E –Latitude: 21°06'11.8"S)

Etymology: The specific epithet palmeti refers to « Plaine des Palmistes » (in latin palmetum) where is located the type locality.

LM Morphology ( Figs 54–63 )

The valves (number of valves observed: 99) are lanceolate, and weakly dorsiventral with the dorsal margin slightly more convex than the ventral margin ( Figs 54–63 ). The apices are short-rostrate and broadly rounded. The axial area is narrow and linear. The raphe is filiform, slightly curved to the ventral side but with dorsally deflected proximal endings terminating in inconspicuous central pores. The striae are parallel in the middle part of the valve and then become weakly radiate.

SEM Morphology ( Figs 64–72 )

Externally, the raphe slit is slightly curved to the ventral side and then becomes deflected to the dorsal side with enlarged proximal endings bent to the dorsal side ( Figs 64–66 ). The terminal fissures are curved towards the ventral side and terminate close to the poles in drop-like endings ( Fig. 66 ). The central area is only distinguished dorsally by three weakly shortened striae ( Fig. 66 ). The striae are composed of apically-elongated areolae sometimes irregular in shape ( Figs 65, 66 ), numbering around 40 in 10 µm. Internally, the raphe fissure is interrupted by an extremely short intermissio ( Fig. 67 ) and the distal endings terminate in well-developed helictoglossae ( Fig. 68 ). The striae form shallow depressions in which the areolae are rounded and occluded ( Fig. 69 ) by “ papillae ”-like structures (Krammer 2002), although they may appear apically elongated when they are partially occluded ( Figs 68–69 ). The raphe ( Fig. 70 , arrow) seems to be of the key and slot type ( Krammer, 1982). As in E. cilaosensis , each level of the cingulum is composed of two opposite bands tapering near the middle of the valve where they fit together with the other bands of a different level ( Figs 71–72 ). The entire cingulum could not be observed.

Ecology and distribution

E. palmeti had a high relative abundance (22%) in the type locality “Ravine de l’Etang à Grand Etang” in slighty alkaline waters (pH 7.5) with low conductivity ( Table 4 ). This species was associated with Achnanthidium catenatum (Bílý & Marvan) Lange-Bertalot (1999: 277) (16%), other Achnanthidium species (34%) and Fragilaria sp. (14%). This species was recorded from four other sites with a very low relative abundance (0.2%).

Figures

FIGURES 54–63. Encyonopsis palmeti LM. Scale bar: 10 µm. Valve views of the holotype population from Ravine de l'Etang à Grand Etang showing variation in size.

FIGURES 64–67. Encyonopsis palmeti SEM.Scale bars:1µm (Figs64–66),100 nm(Fig.67). FIGURE 64. External view of a small specimen. FIGURE 65. External view of a large specimen. FIGURE 66. External view showing the raphe course. FIGURE 67. Internal view of intermissio.

FIGURES 68–72. Encyonopsis palmeti SEM.Scale bars:1µm (Figs68,69and 71),100 nm(Figs 70and72). FIGURE 68. Internal view of the raphe with helictoglossa. FIGURE 69. Internal view showing areolae occluded by “papillae”. FIGURE 70. Internal view of a broken valve showing the key and slot raphe (arrow) and partially occluded areolae. FIGURE 71. Internal view of a valve showing the endings of two copula (C). FIGURE 72. Interlocking system of “half” copulae.