Surirella tayronarum, Tombé & Sala & Vouilloud & Restrepo, 2016

Tombé, Mario Fernando Medina, Sala, Silvia E., Vouilloud, Amelia A. & Restrepo, John Jairo Ramírez, 2016, Surirella tayronarum spec. nov. (Surirellaceae, Bacillariophyta) from Colombia, Phytotaxa 278 (1), pp. 39-47 : 41-42

Surirella tayronarum spec. nov. ( Figs 1–31 )

LM ( Figs 1–17 ): Frustules isopolar in valve and girdle views. Valves parallel, with round apices in girdle view ( Figs 1–2 ). Valve outline panduriform, gently constricted—less evident in smaller specimens—with cuneate apices ( Figs 3–15 ). Valve face strongly undulated transapically, with scattered small granules ( Fig. 16 ); axial area straight with a conspicuous median ridge that does not reach the apices ( Figs 3–4, 6, 7, 9, 10–12, 14, 16–17 ). Wings well developed. Under high magnification, striae ( Fig. 16 ) and long tendrils on the inner side of wings ( Figs 9, 16 , arrowheads) are visible at median area. Girdle with few, broad bands, valvocopula open near the valve center ( Fig. 1 , arrow). SEM ( Figs 18–31 ): Valve face transapically corrugated ( Fig. 18 ). In external view, the median area is elevated at mid-valve and sunken at the poles ( Figs 19–20 ). In internal view, the axial area is markedly sunken but does not reach the apices that are bulky ( Figs 26–27 ). Striae are uniseriate, with circular areolae irregularly arranged, difficult to see even with SEM ( Figs 27–29 ). External valve face covered with small scattered granules ( Figs 19, 20, 22, 23 ). Wings well developed ( Figs 19–21, 24–25 , 30–31 ), fenestrae with 2–8 fenestral bars ( Figs 21, 24, 25 , 31 ). On the base of the fenestrae there are solitary or eventually paired long ribbon-like tendrils with sharp ends ( Figs 18–22 ). Raphe canal smooth ( Fig. 20, 22 ), raphe externally interrupted at both ends, curved towards the mantle and with terminal small elongated pores ( Fig. 25 ). Internally, the mantle and the valve face have the same structure ( Figs 28–29 ) and the alar canals open in simple portulae ( Figs 26–29 ). On the external side, the mantle edge is thickened in a narrow flange with parallel slits and silica plaques ( Figs 24–25 ). Girdle with few, broad, non-perforated bands, valvocopula open near the valve center ( Figs 30–31 ). Morphometric data (n=40): length (μm): 76.5–200.0, average 121.9 ± 28.9 SD; width (μm): 22–31, average 26.2 ± 2.3 SD; l/w: 2.4–6.6, average 4.7 ± 1.1 SD; maximum width (μm): 22.5–44.0, average 32.1, ± 4.6 SD; pervalvar axis (μm): 28.5–36.5; alar canals in 100 μm: 14–22, average 19 ± 1.9 SD; striae in 10 μm: 30–31, average 30.5 ± 0.7 SD; areolae in 10 μm: 45–50, average 47.5 ± 3.5 SD.

Type:— COLOMBIA. Magdalena: Ciénaga, Congo River, 10° 59’ 21.6” N, 74° 4’ 1.6” W, 749 m a.s.l., M.F. Medina Tombé , 2 February 2015 (holotype LPC! 5567 slide 5567(1), finder K 28(3), here illustrated as Figs 12–13 ).

Etymology:— the specific epithet refers to the “Tayrona” indigenous habitants of the region.

Ecological data:— the sites where this species was collected are located between 724 and 939 m a.s.l., at an average temperature of 20 °C, pH of 7.9, conductivity of 110.62 μS cm-1, dissolved oxygen ranging from 6.5 to 8.0 mg L- 1 and a flow of 0.04–1.67 m 3 sec-1.

Distribution:— the species was only found in the five samples collected at the Congo River Basin, Caribbean Region (LPC 5567, 5568, 5569, 5570 and 5571).

Habitat:— epilithic in rivers and streams located between 724 and 939 m a.s.l., at an average temperature of 20 °C, pH of 7.9, conductivity of 110.62 μS cm-1, dissolved oxygen ranging from 6.5 to 8.0 mg L- 1 and a flow of 0.04–1.67 m 3 sec-1.

Remarks:— this taxon belongs to the Robustae group; the most similar taxon is S. rafaelii described from Antioquia, Colombia ( Sala et al. 2013). These two species are isopolar and have the same type of ribbon-like tendrils. Under LM they clearly differ in valve outline ( S. rafaelii is no or poorly constricted at mid-valve) and morphometric data ( Table 2). In addition, they differ in fine valve morphology: externally in the mantle structure with irregular areolation, raphe canal with transversal ribs and eventually grouped tendrils in S. rafaelii ; internally this species does not present the bulky apical areas always seen in S. tayronarum .

Figures

FIGURES 1–17. Surirella tayronarum spec. nov. LM. Specimens of the type population. 1–2. Frustule in girdle view. Note the open of valvocopula (arrow). 3–15. Valve views showing shape and size variation. 16. Detail of valve showing striae, granules and tendrils (arrowheads). 17. Detail showing the sunken end. 12–13. Holotype. Scale bars: Figs 1–15: 20 μm, Figs 16–17: 10 μm.

FIGURES 18–25. Surirella tayronarum spec. nov. SEM. 18–23. Valves in external view. 18. View of the whole valve, note the elevated median ridge and the sunken end. 19. Detail of the valve end showing median ridge, fenestrae and tendrils. 20. Valve end showing median ridge, raphe canal and granules. 21. Detail of the wing, showing the fenestrae and tendrils. 22. Detail of the valve face. Note smooth raphe canal, fenestrae, tendrils and granules. 23. Detail of the granules. 24. Detail of the mantle, note the line of slits and silica plaques. 25. Valve in girdle view, detail of the pole showing the expanded raphe end. Scale bars: Fig. 18: 20 μm, Figs 19–20: 10 μm, Figs 21–22, 24–25: 2 μm, Fig. 23: 1 μm.

FIGURES 26–31. Surirella tayronarum spec. nov. SEM. 26–29. Valves in internal view. 26. View of the whole valve. Note the sunken axial line and the bulky end. 27. Detail of the valve end showing portulae and striae with tiny areolae. 28. Detail showing the tiny areola arranged in sinuous lines. 29. Detail of portulae, note the internal raphe fissure. 30–31. Frustule in girdle view. 30. View of the whole frustule. 31. Detail showing the unornamented open girdle bands. Scale bars: Fig. 26: 20 μm, Fig. 30: 10 μm, Figs 27–31: 3 μm, Figs 28–29: 1 μm.