Achnanthidium minutissimum (Kütz.) Czarn.

(Fig. 14)

Memoirs of the California Academy of Sciences 17: 157 (Czarnecki 1994). — Basionym: Achnanthes minutissima Kütz., Linnaea 8 (5): 578, pl. 16, fig. 54 (Kützing 1833); Kützing, 50, pl. 4, fig. 54 (Kützing 1834); Kützing, Dec. VIII, no. 75 (Kützing 1834), in Kützing, Algarum Aquae Dulcis Germanicum, Decades I-XVI, numbers 1-160. Halis Saxonum, 1833-1836.

DESCRIPTION

LM (Fig. 14 A-AW)

Frustules slightly arched, with convex RL, concave RV. Valves linear-lanceolate. Margins tapering gradually towards short protracted rounded, rostrate poles. Valve dimensions (n = 46): length 8.5-15 µm, width 2.5-3.5 µm. Central area on raphe valve varies from small rounded to a narrow rectangular fascia on one or both sides. Striae more widely spaced in valve centre. Raphe filiform, straight, central pores slightly widened, terminating close to margin of central area. Central area on rapheless valve indistinct or narrow elliptical. Axial area narrow linear on both valves, slightly widening towards valve centre. Striae radiate throughout on both valves, 30-35 in 10 µm (RV and RL), becoming denser at poles.