Fragilaria billingsii Wengrat, C.E. Wetzel & E. Morales, 2016

Wengrat, Simone, Morales, Eduardo A., Wetzel, Carlos E., Almeida, Pryscilla D., Ector, Luc & Bicudo, Denise C., 2016, Taxonomy and ecology of Fragilaria billingsii sp. nov. and analysis of type material of Synedra rumpens var. fusa (Fragilariaceae, Bacillariophyta) from Brazil, Phytotaxa 270 (3), pp. 191-202 : 196-198

Fragilaria billingsii Wengrat, C.E. Wetzel & E. Morales , sp. nov. ( Figs 22–41 )

Valves are long, narrow, lanceolate, gradually tapering toward the apices and with subcapitate ends ( Figs 22–34 ). Length 54.0–76.0 μm, width 2.0–2.5 μm. The central valve margin is inflated on both sides of the valves. The axial area is lanceolate, with clear fascia at the valve center. Striae are distinct, parallel and alternate throughout the valve, 17–20 in 10 μm. Areolae not discernible in LM. Ribbon-like colonies were not observed. SEM: External SEM images show striae composed of round or apically elongated areolae ( Figs 35–37 ). Striae are interrupted by spines and continue to the mantle ( Fig. 36 ). Striae are parallel throughout the valve and composed of single areolae at the apices, increasing to up to five toward the valve center ( Figs 35–37 ). Costae are wider than the striae and are clearly raised at the middle of the valve and only slightly raised toward the apices ( Figs 35–37 ). Spines are angular to pyramidal with acute ends ( Figs 35–37 ); two to five spines are found at the each apex ( Figs 37, 39 ). Spines are present along the valve face margin ( Figs 35, 36 ). Well-developed apical pore fields of the ocellulimbus type, with round poroids are present on the mantle at both valve ends ( Figs 37, 39 ). Plaques are present along the abvalvar margin of the mantle ( Fig. 36 ). Girdle bands open (not shown here). Internal SEM images show one rimoportula per valve, located on the axial area ( Figs 40, 41 ). The abvalvar margin of the mantle thickened at the valve apices.

Type: — BRAZIL. São Paulo: Rio Grande Reservoir, 23° 46.124’ S, 46° 31.792’ W, S. Wengrat & D. C. Bicudo, 11 February 2011 (holotype SP!, population on slide SP401572, illustrated here in LM as Figs 22–34 . Paratype SP! population on slide SP427907, illustrated here in SEM as Figs 35–41 . Isotype BR!, population on slide BR-4429).

Etymology: —The species is named after the Billings Reservoir, an important multipurpose water body for the Metropolitan Region of São Paulo.

Distribution and ecology: — Fragilaria billingsii was found in phytoplankton and periphyton from meso-eutrophic reservoirs with slightly acidic pH 6.2–6.4, low conductivity 45–64 μS cm-1, high temperature 24–26 °C, and slightly enriched waters TP: 23.9–26.6 μg L- 1, NT: 426–1459 μg L- 1 ( Table 1). Fragilaria billingsii occurred in high abundance (9.5% to 37.4%) and was found associated with Achnanthidium catenatum ( Bílý & Marvan 1959: 35) Lange-Bertalot (1999: 277) , Fragilaria aquaplus Lange-Bertalot in Lange-Bertalot & Ulrich (2014: 32) and Discostella stelligera (Cleve & Grunow in Cleve 1881: 22) Houk & Klee (2004: 208).

Remarks: — Fragilaria billingsii is quite similar to F. fusa especially by the long and narrow valves, and the inflated central area. However, they can be distinguished mainly based on the higher striae density (17.0–20.0 μm), narrower valves (2.0–2.5 μm), pyramidal shape of the spines, and less developed rimoportula of F. billingsii . The new species can also be misidentified as F. tenera , but the latter has most frequently parallel margins or sometimes slightly inflated at the central area and spines have a sharp cone appearance ( Table 2). Although Smith’s original description of F. tenera shows higher striae density (24/10 μm), F. tenera was latter lectotypified by Krammer & Lange-Bertalot (1991, pl. 115, figs 1–2) and recently re-analyzed in more detail by Lange-Bertalot & Ulrich (2014) and Almeida et al. (2016). According to the last reference, specimens of F. tenera were abundant in the lectotype material, which allowed to provide more detailed measures. Additionally, F. billingsii differs from F. parva and F. pararumpens mainly by its subcapitate valve ends and longer valves (72.0–86.0 μm), while F. parva and F. pararumpens have capitate ends and shorter valves (33.0–41.5 μm and 25.0–50.0 μm, respectively) ( Table 2). Fragilaria billingsii belongs to the needle-shaped Fragilaria group, similar to Fragilaria neotropica P.D. Almeida, E. Morales & C.E. Wetzel in Almeida et al. (2016: 171, figs 23–53), illustrated as Fragilaria sp. by Almeida & Bicudo (2014: 194, figs 17–19) and commonly found in São Paulo State reservoirs.

Concerning the ecological preferences, several new species have been described from oligotrophic and clear waters from Brazil (e. g. Metzeltin & Lange-Bertalot 2007, Tremarin et al. 2015, Almeida et al. 2016), and just a few from eutrophic environments (e. g. Wetzel & Ector 2014). The present work reports a new taxon found as abundant in a well-known and multipurpose reservoir from São Paulo (e. g. Beyruth & Pereira 2002, Capobianco & Wathely 2002) in meso-eutrophic sites induced by algaecide addition ( Wengrat & Bicudo 2011). The new species was also found in other eutrophic reservoir (Jundiaí) from the Upper Tietê River Basin in periphyton and phytoplankton. Therefore, F. billingsii was found living in slightly acidic waters with moderate to high nutrient enrichment. This finding suggests that greater efforts could yield additional taxa new to science, thus increasing our knowledge of diatom diversity in South America and tropical regions. Besides, the associated ecological information would improve the potential use of the species in bioindication studies.

Figures

FIGURES 22–34. Type material of Fragilaria billingsii. All pictures taken from the holotype population (SP401572). Light microscopy showing variation in size and valve outline. Scale bar = 10 μm.

FIGURES 35–41. Type material of Fragilaria billingsii. All pictures taken from the paratype population (SP427907). Scanning electron micrographs. 35, 36. External view showing the striae, areolae, spine structure and mantle. 37, 39. External view of apical pore fields. 38, 40, 41. Internal view of areolae and rimoportula.