Encyonopsis sanctipaulensis Wengrat, Marquardt & C.E. Wetzel, 2015

Wengrat, Simone, Marquardt, Gisele C., Bicudo, Denise C., Bicudo, Carlos E. De M., Wetzel, Carlos E. & Ector, Luc, 2015, Type analysis of Cymbella schubartii and two new Encyonopsis species (Bacillariophyceae) from southeastern Brazil, Phytotaxa 221 (3), pp. 247-264 : 254

Encyonopsis sanctipaulensis Wengrat, Marquardt & C.E. Wetzel , sp. nov. ( Figs 36–54 )

Light microscopy ( Figs 36–50 ): valves slightly asymmetric, slightly dorsiventral, elliptic-lanceolate, dorsal and ventral margins slightly convex. Apices rounded, rostrate, mostly slightly curved to the ventral margin. Length 21.4–32.0 μm, width 5.2–6.5 μm, l/w ratio 4.1–5.4. Axial area moderately narrow, lanceolate, gradually widening towards the median region of valve. Central area absent. Raphe branches straight or faintly undulate, linear, approximately in the median region of the valve; proximal ends slightly rounded, dorsally bent; terminal fissures indistinct or ventrally bent. Striae almost parallel to weakly radiate in the center, becoming radiate towards the apices. Dorsal striae 9–11 in 10 μm, ventral striae 9–11 in 10 μm, at the ends 10–11 (12) striae in 10 μm; areolae not discernible in LM; stigmoid absent. Scanning electron microscopy ( Figs 51–54 ): striae uniseriate composed by elongate foramina appearing as narrow slits ( Figs 51–52 ), turning shorter towards the apices. Stigmoid absent. Raphe slightly sinuous externally, curved to the dorsal side at the center, terminating in expanded, very weakly deflected pores ( Fig. 52 ); terminal fissures hooked towards the ventral margin ( Fig. 52 ). Inner raphe fissure straight, with an intermissio near the central nodule ( Fig. 53 ). Distal raphe endings terminating in helictoglossae ( Fig. 54 ). Internal areolae: struts provide structural support to the foramen, whose opening bears three spines at each side ( Fig. 54 ). 34–36 areolae in 10 μm.

Type: — BRAZIL. São Paulo: Billings Reservoir, Rio Pequeno branch, 23° 47.027’ S, 46° 26.188’ W, S. Wengrat & D. Bicudo, 6 August 2009 (holotype SP!, slide 401589, Herbário Científico do Estado Maria Eneyda P. Kauffmann Fidalgo, São Paulo, Brazil, depicted in Figs 36–50 . Isotype BR!, slide 4422, Botanic Garden, Meise, Belgium).

Etymology: —From São Paulo State, where the collecting sites are located.

Morphological examination: —The benthic populations from Ribeirão do Campo Reservoir showed more stable morphological characteristics ( Figs 36–40 ). However, the populations from Billings Reservoir included some smaller individuals, some of them with more symmetrical valves and more extended apices, and some others with more asymmetrical valves, with shortened subrostrate apices ( Figs 46–50 ). Both populations showed, however, a continuous range of morphological features and striation pattern evidencing their conspecificity.

Although having similar valve length, E. sanctipaulensis and E. subcapitata Krammer (1997b : fig. 180: 1–4) can be distinguished from one another mainly by the shape of their valve apices: E. sanctipaulensis has more rostrate, elongated and protracted apices, while E. subcapitata is subcapitate, especially in larger specimens. In addition, valves of E. subcapitata are wider (8–9 μm) and have less striae in 10 μm (8–9). The valve apices may also distinguish E. sanctipaulensis from E. schubartii and E. difficilis . Encyonopsis schubartii has subcapitate to capitate valve ends, besides, the axial area is narrower and less lanceolate than in E. sanctipaulensis , while E. difficilis has more asymmetric valves and rounded, subrostrate apices. Furthermore, E. sanctipaulensis areolae ultrastructure is lineolate and internally supported by struts, whereas E. difficilis has round to rounded lineolae (not slits) not supported by internal struts.

Encyonopsis sanctipaulensis can also be misidentified as E. difficiliformis ( Krammer 1997b: figs 162: 25–26; 202: 7–12a), but the last has wider valves (6.7–7.8 μm) and lower length:width ratio (maximum 4.7, according to Krammer 1997b). Based on the morphological differences above, separation of both species is justified.

Ecology: —The new species was common in samples collected from the surface sediments of two reservoirs in the State of São Paulo (Rio Pequeno branch of Billings Reservoir, relative abundance 12.0 %, and Ribeirão do Campo Reservoir, 6.7 %) and a sediment core from the last one (7.6 % at the top and 18.0 % at the bottom). The first reservoir is oligo-mesotrophic, with acidic pH (5.1), low conductivity (31–32 μS cm-1) and low nutrient concentrations (TP 10 μg L- 1, NT 298 μg L- 1). Ribeirão do Campo is oligotrophic, with acidic pH (5.4), low conductivity (11–12 μS cm-1) and low nutrient concentrations (TP 4.0–4.7 μg L- 1, TN 355–362 μg L- 1). The new species was abundant in surface sediments, and in the top and bottom samples of a sediment core. Encyonopsis sanctipaulensis was collected associated with Brachysira brebissonii , Eunotia veneris and Frustulia crassinervia .

Figures

FIGURES 36–54. Encyonopsis sanctipaulensis. 36–40. LM views showing variation in size and valve outline of the Ribeirão do Campo Reservoir population. 41–54. Type material of Encyonopsis sanctipaulensis. All pictures taken from the holotype population (SP401589). Light and scanning electron micrographs. 41–50. LM views showing variation in size and valve outline. 51. SEM external view of areolae and central area. 52. SEM external view of entire valve showing the raphe and striae structure. 53. SEM internal view of central area. Note the intermissio. 54. SEM internal detail of valve apex with helictoglossa. LM scale bar = 10 μm (in Figs 36–50).