Odontidium andinum, Sala & Vouilloud, 2018

Sala, Silvia E. & Vouilloud, Amelia A., 2018, Odontidium andinum spec. nov. (Bacillariophyta) from Mendoza, Argentina, Phytotaxa 372 (3), pp. 221-228 : 222-225

Odontidium andinum spec. nov. Vouilloud & S. Sala ( Figs 1–54 )

Frustules square to rectangular in girdle view ( Figs 1–7 ). Valves broadly lanceolate in smaller specimens, linear to slightly constricted in larger specimens; poles protracted, rounded to subcapitate ( Figs 8–27, 32–37, 34–36 ). Sternum slightly eccentric, narrow, visible with LM ( Figs 14–18, 21, 23–24 ). Uniseriate striae composed of circular areolae, parallel at center, slightly radial to poles ( Figs 25–30 ). Primary and secondary ribs prominent, irregularly spaced ( Figs 8–24 , 34–38, 41 ); externally visible as wider virga ( Fig. 30 , arrows), internally heavily silicified, extending on to valve face and mantle ( Figs 34–42 ). Apical pore-fields well developed, occupying part of valve face; sternum extending into pore-field; poroids very small and radially arranged from sternum and extending around the apices ( Figs 31 , 40 ). One rimoportula per valve situated within a stria adjacent to distal rib and sternum, externally visible as small hole ( Figs 25, 28–29, 31 ), internally as small, paired lips ( Figs 34, 40 ). Small conspicuous conical spines at valve face/margin boundary, either single or several grouped ( Fig. 30 ); a few larger spines occur on surface of pore-field, at its end ( Fig. 31 ). Valve mantle with striae arranged in flabelliform groups ( Figs 33 , 43 ). Cingulum composed of several open copulae (c. 10) ( Figs 1–7 ). Larger specimens with thin and almost straight copulae, only moderately arcuate at poles ( Figs 4–7 ); smaller specimens with strongly curved copulae ( Figs 1–3 ). Valvocopula with ligula, one complete row of poroids on pars interior ( Figs 43–46, 49 arrowheads) and one discontinuous row on pars exterior ( Figs 43–45, 47, 49 arrows); proximal edge of pars interior with valvocopular extensions overlapping and gripping each transapical rib ( Figs 21–22 , 37 and 39 , arrows), smaller fringe attached to virgae (42, arrowheads), visible with LM ( Figs 16, 21, 24 ). Other copulae similar, with ligula and one row of poroids on pars interior, second row on pars exterior, with several rows at poles ( Figs 50–51 ). Pleurae narrower with slightly curved ends, with one row of poroids on pars media and a small ligula ( Figs 52–54 ). All cingular elements with granules of silica on pars exterior ( Figs 32–33 , 53–54 ).

Morphometric data: (n= 50): pervalvar axis: 9–13 μm; length: 14–66 μm; breadth: 8–10 μm; l/b: 2.7–7.5; 3–4 ribs in 10 μm; 20–25 striae in 10 μm; 5–10 striae between ribs; 52–59 areolae in 10 μm; 56–62 areolae in 10 μm at the cingular bands (pars exterior of the copula).

Type:— ARGENTINA. Mendoza: Vega del Río Diamante. Guerrero, 21 March 1999 (holotype LPC! 7479 slide 7479 (4), finder Q 44(4), here illustrated as Fig. 14 ).

Marked Isotypes: Fig. 12 : Slide 7479(3) Finder M 38(2/4) ; Fig. 16 : Slide 7479 (3) Finder L 37(4) ; Fig. 17 : Slide 7479 (3) Finder L 35(4) ; Fig. 22–23 : Slide 7479 (3) Finder R 48 (4) ; Fig. 24 : Slide 7479 (3) Finder J 47(3)

Etymology: — The specific epithet refers to the distribution of the species in the Andean region.

Remarks: — Rumrich et al. (2000: Taf. 2, Figs 3–7 ) illustrated several specimens they names Diatoma hyemalis (Roth) Heiberg sensu lato. Rumrich et al. made no comments on their specimens, providing no description but in our view these are example of O. andinum as the morphometric data and valve outline is the same. Therefore we consider them to be examples of O. andinum .

O. andinum has an Andean distribution. Until now it was found in Mendoza province at the Diamante River basin (this study). The specimens reported by Rumrich et. al. (2000) were collected at the Nauto River (1600 m asl) and Felsen and Serrano Glaciers in Chilean Patagonia. Recently we found it in a sample collected in Cañon of River Chico, Chubut Province, Argentinean Patagonia (unpublished data).

Figures

FIGURES 1–24. Odontidium andinum spec. nov. LM. Specimens of the type population. 1–7. Frustules in girdle view. 8–24. Valve views showing shape and size variation. The arrowheads in Figs 16, 21, 24 show the lobules attached to the virgae and the arrows in Figs 21, 22 show the valvocopular extensions of the pars interior gripping each transapical rib. Fig. 14. Holotype. Figs 12, 16, 17, 22–23, 24. Isotypes marked with Finder. Scale bars: 10 μm.

FIGURES 25–33. Odontidium andinum spec. nov. SEM. 25–29. Valves in external view. 30. Detail of the valve center; note the narrow flat sternum, the small areolae of the striae and the spines near the valve margin; the arrows show the position of the internal transapical ribs. 31. Detail of the valve end; note the external opening of the rimoportula, the sternum extending into the porefield and the marginal spines. 32. Detail of valve mantle and valvocopula ends. 33. Detail of valve mantle and the valvocopula in external view; note the mantle striae arranged in flabelliform groups. Scale bars: 25–29= 10 μm; 30–33: 2 μm.

FIGURES 34–42. Odontidium andinum spec.nov.SEM. 34–37.Whole valves in internal view; note the presence of primary and secondary transapical ribs; the arrows in Fig. 37 show the valvocopular extensions of the pars interior gripping each transapical rib. 38. Detail of valve center. 39. Detail of the valvocopular extensions of the pars interior gripping each transapical ribs (arrows). 40. Detail of the valve end; note the internal opening of rimoportula and the sternum extended into the porefield. 41. Whole valve in internal oblique view, note the flat sternum. 42. Detail of valvocopula in internal view showing the valvocopular lobules attached to the virgae (arrowheads). Scale bars: 34–37, 41= 10 μm; 38–40, 42= 2 μm.

FIGURES 43–54. Odontidium andinum spec. nov. SEM. 43. Detail of the valve and valvocopula. 44. Mantle with valvocopula and copula associated, note the granules and the discontinuous row of poroids on the pars exterior. 45. Mantle end with valvocopula and associated copula. 46. Frustule end showing the open valvocopula. 47. Valvocopula, note the extensions of the pars interior, the rows of poroids and the granules in the external side of the pars exterior. 48. Detail of the ligula of the valvocopula. 49. Detail of the valvocopula in internal view, note the poroids of the pars interior (arrowheads) and the pars exterior (arrows). 50. Copula, note the line of poroids of the pars interior. 51. Detail of the previous figure, note the ligula. 52. Pleura. 53–54. Detail of the previous figure showing the ligula (fig. 53); note the row of poroids of the pars media and the granules of the pars exterior. Scale bars: 47, 50, 52= 10 μm; 43–46, 48–48, 49, 51, 53–54= 2 μm.