Achnanthidium Exiguum Guide
Credit: Marina Potapova
  1. Valves with capitate to subrostrate apices
  2. Raphe valve with fascia
  3. Rapheless valve with small transversely rectangular central area
  4. Striae more dense on raphe valve than on rapheless valve
  5. Terminal raphe ends curved to opposite sides

Valves are linear-elliptic to elliptic-lanceolate, with narrowly capitate to subrostrate apices. The raphe valve has a distinct fascia. The rapheless valve has a small, transapically rectangular central area. The raphe is straight, but deflected to opposite sides near the apices. The terminal raphe fissures are strongly curved to opposite sides. The central external raphe ends appear to be expanded. The striae are radiate on both valves, but almost parallel at the apices.