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

Figs 6J-O (LM), 9A-F (SEM)

Holotype.

Slide BR-4679, Fig. 6K, 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 lanceolate, isopolar with semi-gradual transition from valve face to mantle. Valve apices subrostrate with broadly rounded, somewhat squarish ends (Figs 6J-O, 9A-D). Axial area lanceolate (Fig. 6J-O), externally and internally faintly depressed with respect to virgae (Fig. 9A-D). Vimines short and wide (Fig. 9A, B). Striae composed of round to elliptic areolae, decreasing in size towards the axial area (Fig. 9A, B); wide elliptical areolae present toward valve face/mantle transition before and after the spine, sometimes accompanied by a narrower additional areola on valve mantle (Fig. 9E, F). Striae contained in a single depression in internal view (Fig. 9C, D). Well-developed volae, arising from the areolar inner periphery and projecting inwards (Fig. 9B-D). Flaps small and present on some valve face areolae (Fig. 9A, B), more commonly on larger mantle areolae (Fig. 9D-F). Spines originating from vimines at the valve face/mantle junction; solid, with round to elliptical base (Fig. 9A, B), as wide as the vimines they sit on (Fig. 9A, B, E); with cylindrical body and shallow concave sides (Fig. 9E, F), and spatulate tip with lateral projections and a serrate border pattern (Fig. 9D-F). Stipules incipient and subtending a small circular depression on the spine upper body (Fig. 9D, F). Apical pore fields covered by external flaps (Fig. 9A, E, F). Internally, apical pore field opening into roundish depression, revealing several rows of round poroids (Fig. 9D). Well-developed blister-like depositions present on abvalvar edge of mantle also covering both apices (Fig. 9D-F). Girdle elements variable in number, open, lacking pores, ligulated, with larger valvocopula (Fig. 9E, F).

Dimensions (n> 30): Length 6.7-35.6 μm; width 3.3-3.8 μm; striae 14-16 in 10 μm .

Etymology.

The species epithet alludes to the fact that this diatom has remained unidentified thus far and has been confused with morphologically similar taxa (see Discussion).

Distribution.

Found in the Sajama River.