Encyonema acquasedis Marquardt, A.

Marquardt, Gisele C., Da Rocha, Angélica C. R., Wetzel, Carlos E., Ector, Luc & Bicudo, Carlos E. De M., 2016, Encyonema aquasedis sp. nov. and Kurtkrammeria salesopolensis sp. nov.: two new freshwater diatom species (Cymbellales, Bacillariophyceae) from an oligotrophic reservoir in southeastern Brazil, Phytotaxa 247 (1), pp. 62-74 : 64-66

Encyonema acquasedis Marquardt, A. Rocha & C.E.Wetzel, sp. nov. ( Figs 2–11 , 24–31 )

Valves linear-lanceolate, not or weakly dorsiventral. Length 28.0–67.4 μm. Breadth 4.8–6.4 μm. Dorsal side slightly convex, ventral side slightly convex to straight, sometimes slightly expanded. Apices narrow, rounded. Raphe filiform, slightly lateral, with proximal fissures weakly expanded, curved to the dorsal margin; distal raphe ends comma-shaped, sharply bent to the ventral margin. Axial area narrow, linear, slightly broader on the ventral margin. Central area not distinct. Striae uniseriate, slightly radiate, 9–10/10 μm. Areolae apically elongate rounded or “Y” disposed visible only in the SEM, approximately 40 in 10 μm. Shortened striae continuing around valve apices. Isolate punctum not discernible.

Type:— BRAZIL. São Paulo (SP), Salesópolis: Ribeirão do Campo reservoir, sediment core, 23º 38.514’ S, 45º 49.854’ W, 886 m a.s.l. A. C. R. Rocha & D. C. Bicudo, 13 August 2010 (holotype: SP!, slide 427990, here depicted in Figs 2–11 . Isotype: BR! slide 4430).

Etymology:—The specific epithet refers to the research project acronym AcquaSed: “Base line diagnosis and reconstruction of anthropogenic impacts in the Guarapiranga Reservoir, focusing on the sustainability in water supply and water quality management in reservoirs of the Alto Tietê and surrounding basins”, in which this study is included.

Additional morphological data:—External raphe fissures are slightly undulate ( Fig. 24 ), slightly closer to the ventral margin, while the internal slits are straight ( Fig. 27 ). Proximal ends of raphe are almost straight, the enlarged proximal endings slightly curved to the dorsal side ( Figs 24, 26 ). Distal raphe ends are comma-shaped, first dorsally bent, and then strongly hooked to the ventral side ending onto the mantle ( Figs 24, 25 ). Axial area is narrow, linear ( Fig. 24 ). Central area absent. Striae uniseriate, slightly radiate composed of apically-elongated lineolate areolae, some rounded areolae at the end of the stria ( Figs 24–26 ) sometimes “Y” disposed ( Fig. 26 ) numbering 40 in 10 μm. Transapically shortened striae composed of one lineolate and another rounded areolae continuing around the apex ( Figs 24–25 ). Internal striae are lineolate and positioned between thickened internal costae ( Figs 27–31 ) numbering 9–10 in 10 μm. Internally, there is a fissure located at the proximal end of the median dorsal stria ( Figs 27–29 ) but externally, isolated puncti were not observed ( Figs 24, 26 ). Separation of internal proximal raphe ends hooked strongly towards the dorsal margin, forming a very narrow intermissio ( Figs 27–29 ) and the distal endings terminate in well-developed helictoglossae that are deflected towards the ventral margin ( Figs 27, 30–31 ).

Figures

FIGURES 2–23. Light micrographs. 2–11. Encyononema acquasedis. LM views showing variation in size and valve outline. 12–23. Kurtkrammeria salesopolensis. LM views showing variation in size and valve outline. Scale bars = 10 μm. Populations from type material SP427990 (surface sediments).

FIGURES 24–31. Scanning electron micrographs. Encyononema acquasedis. Population from type material (SP427990). 24–26. SEM external view of entire valve showing raphe and striae structure. 27. SEM internal view of entire valve showing raphe and striae structure. 28, 29. SEM internal detail of isolated punctum fissure and central area forming a very narrow intermissio. Note the areolae with struts providing structural support to the foramen. 30, 31. SEM internal detail of valve apex with helictoglossa.