Pseudostaurosira oblonga E. Morales, C.E. Wetzel & Ector sp. nov.

Figs 6P-V (LM), 10A-F (SEM)

Holotype.

Slide BR-4680, Fig. 6R, Meise Botanic Garden, Belgium. Isotype. Slide DBOL-0249a, Diatomotheca Boliviensis (before HCUCB), Cochabamba, Bolivia.

Type locality.

Bolivia. Sajama Province, Department of Oruro, Sajama River, epipsammon, 17°30'33"S; 68°20'35"W, 4000 m elev., leg. G. Chávez, 05.07.2009.

Description.

Frustules rectangular in girdle view, joined together by interlocking spines. Valves oblong, isopolar, with abrupt transition from valve face to mantle and broadly rounded apices (Figs 6P-V, 10A-F). Axial area lanceolate (Figs 6P-V), externally and internally depressed with respect to virgae (Figs 10A-F). Vimines short and wide (Fig. 10A-F). Striae composed of round to elliptic areolae, decreasing in size towards the axial area (Fig. 10A, B); wide trapezoid areolae present near the valve face/mantle transition at the base of the spine, sometimes accompanied by an additional narrower, round areola on valve mantle (Fig. 10A-F). Striae contained in a single depression in internal view (Fig. 10C, E). Developed volae, arising from the areolar inner periphery and projecting inwards (Fig. 10A, C, E). Flaps little-developed on valve face, developed on valve mantle, more commonly on larger mantle areolae (Fig. 10A, F). Spines originating from vimines at the valve face/mantle junction; solid, with elliptic base (Fig. 10F), as wide as the vimines they sit on (Fig. 10A, B, F); with a somewhat cylindrical body, concave sides, in the shape of a trapezium in side view (Fig. 10D, F), and widely spatulate tip with wide lateral projections (Fig. 10F). Stipules incipient or absent (Fig. 10A, D, F). Apical pore fields reduced, covered by small external flaps (Fig. 10A, B, F). Internally, apical pore field opening by means of a few very narrow, round poroids (Figs 10C). Small blister-like depositions present on abvalvar edge of mantle, absent from apices (Fig. 10A, D, F). Girdle elements variable in number, open, lacking pores, ligulated, with larger valvocopula (Fig. 10D, F).

Dimensions (n> 30): Length 6.9-13.5 μm; width 3.8-4.8 μm; striae 13-14 in 10 μm .

Etymology.

The species epithet refers to the widely ellipsoidal valve outline typical of this taxon.

Distribution.

Found in the Sajama River.