Staurosirella paranaensis N.C.Osório, Ector, L.Rodrigues, C.E.Wetzel, 2021

Osório, Nicolli C., Ector, Luc, Rodrigues, Liliana & Wetzel, Carlos E., 2021, Staurosirella paranaensis sp. nov., a new epiphytic freshwater diatom (Bacillariophyceae) from the Paraná River floodplain, Brazil, South America, Phytotaxa 480 (2), pp. 163-173 : 167-169

Staurosirella paranaensis N.C.Osório, Ector, L.Rodrigues, C.E.Wetzel , sp. nov. (LM, Figs 2–34 , SEM, Figs 35–50 )

Frustules rectangular in girdle view, joined by interlocking spines. Valves elliptical, most frequently isopolar to rarely slightly heteropolar with rounded apices. Axial area narrowly lanceolate giving sometimes the impression of having a zig-zag shape. Virgae doubly flared, internally, axial area and virgae are raised leaving the striae in depressions. Vimines long and narrow becoming shorter toward the sternum. Striae running uninterrupted from valve face to mantle. Volae branched and originated from the sides of the areolae projected towards the valve interior. Solid and thin spines, and there are one per costae it originating from one point on each virgae at the valve face-mantle junction, initially hollow then becoming an apically elongated structure with a lamina that becomes spatulate with two prominences in shape at the top. Apical pore fields located on the valve mantle, reaching the valve face-mantle junction at the polar nodules and isolated from neighboring striae, usually equally developed on both valve poles composed of round poroids. Girdle elements variable in number, open, lacking pores, ligulated, and with valvocopula being larger.

Dimensions (n>100): —Length 6–10 µm; width 3.0–4.5 µm; 8–11 striae per 10 µm; mantle depth 2.5–3.5 µm.

Type: — BRAZIL. Paraná: Porto Rico, Garças Lagoon, Upper Paraná River Floodplain , lake, epiphyton, 22°43’27.18”S, 53°13’4.56”W, August 2019, N.C. Osório (holotype: BR! 4609, here illustrated in Fig. 21 ) .

Etymology: —This species is named in honor of the Brazilian state where it was discovered. It comes from the Tupy–Guarani native language referring the river “as large as the sea” (i.e. Pará +nã).

Taxonomic remarks: — Staurosirella paranaensis show similarities with the species listed in the Table 1 . Smaller individuals of S. paranaensis resemble in LM the smaller specimens of Staurosirella martyi (Héribaud) E.Morales & Manoylov , Staurosirella ovata (E.Morales) E.Morales & Manoylov and Staurosirella dubia (Grunow) E.Morales & Manoylov. However , differences in valve outline are clearly visible among them. In addition, other characteristics clearly distinguish them in SEM, and may highlight as more evident the absence of spines in S. martyi and S. ovata and solid spines with two per costae in S. dubia , while S. paranaensis have only one spine per costae. Staurosirella paranaensis also share characters with the small individuals of Staurosirella neopinnata E.Morales, C.E.Wetzel, E.Y.Haworth & Ector ( Morales et al. 2019: 82). These two species have differences mainly in relation to spines, size and girdle bands. Staurosirella neopinnata presents spines originating from two (rarely three) points on each virgae and valves larger than S. paranaensis with an array of different girdle bands. Although they are of distinct genus and share unique taxonomic characters of each genus, S. paranaensis bears a resemblance to Staurosira kjotsunarum E.Morales, Novais & Ector when viewed in LM. Staurosirella paranaensis has slit-like areolae and wide valvocopulae while these characteristics are not observed in Staurosira kjotsunarum.

Ecology and associated diatom flora: — Staurosirella paranaensis was found in a mesotrophic lake, located in the Upper Paraná River floodplain. The environment is characterized by a neutral pH: 6.9 ± 0.06, temperature: 26ºC ± 0.44, dissolved oxygen: 6.29 mg L- 1 ± 0.17, Secchi: 1 m ± 0.07, water depth: 297.7 cm ± 10.7 and median values of nutrients with total nitrogen: 568 µg-1 ± 29.7 and total phosphorus: 39 µg-1 ± 4.25, characterizing mesotrophic conditions. Staurosirella paranaensis is a common species found in epiphytic samples in this floodplain. Both in LM and in SEM we found this species free and also forming colonies with the valves adjoined by spines. We observe chains of up to 4 individuals (after treatment, no live material was observed for this study). The most common species founded in the samples were (by order of relative abundance): Aulacoseira ambigua (Grunow) Simonsen (1979: 56) , Discostella stelligera (Cleve & Grunow) Houk & Klee (2004: 208) , Pinnularia divergens W. Smith (1853: 57) and Sellaphora densistriata (Lange-Bertalot & Metzeltin) Lange-Bertalot & Metzeltin in Metzeltin & Lange-Bertalot (2003: 58). We also observed a negative relationship with two other common species: Achnanthidium tropicocatenatum Marquardt, C.E.Wetzel & Ector in Marquardt et al. (2017b: 318) and Gomphonema subtile Ehrenberg (1843: 416) ; both species decrease in abundance when S. paranaensis is present in the epiphyton.

Figures

FIGURES 2–38. LM. Staurosirella paranaensis sp. nov. from type material. 2–34. LM. 2–9, 13–34. Valve view. 10–12. Girdle view. 35– 38. SEM–External view. Valve views depicting characteristics of the central narrow sternum, striae, and apical pore fields. Vimines long and narrow becoming shorter toward the sternum. Striae running uninterrupted from valve face to mantle, with areolae slit-like. 36–37. Apical pore fields. Broken spines suggesting initially hollow then becoming a solid structure. LM scale bar 10 μm, in SEM the scale bars are identified in the images. Figure 21* indicates the holotype specimen.

FIGURES 39–44. SEM. Staurosirella paranaensis sp. nov. from type material. 39–41. Girdle view of a complete frustule showing wider valvocopulae still attached to both valves. 42. Union of two valves by spines and formation of colonies. 43. Spines detail showing solid spines and an apically elongated structure with a lamina that becomes spatulate with two prominences in shape at the top. 44. View of the spine’s junction of copula, spines terminating near or over the neighboring valve areolae. Scale bars are identified in the SEM images.

FIGURES 45–50. SEM. Staurosirella paranaensis sp. nov. from type material. 45–50. Internal view. 47. Virgae doubly flared, internally, axial area and virgae are raised leaving the striae in depressions. 48–50. Volae branched and originated from the sides of the areolae projected towards the valve interior. Scale bars are identified in the SEM images.