Achnanthes inflata

Frustules are heterovalvar with a raphe valve and a rapheless valve. The valves are triundulate with the central valve margin wider than the apices, which are broadly rounded and capitate. Both valves are symmetric about the apical and transapical axes. The raphe valve face is concave about the transapical axis. On the raphe valve, the axial area is centered on the apical axis. The axial area is linear but narrows at the distal ends. A distinct transverse fascia is present in the central area. The raphe is slightly reverse lateral with expanded proximal ends. The proximal ends are unilaterally deflected. The distal raphe ends are deflected in the opposite direction. The distinctly uniseriate, punctate striae on the raphe valve are slightly radiate throughout and evenly spaced, 11 in 10 µm. The rapheless valve is convex about the transapical axis and does not have a fascia. On the rapheless valve, the narrow sternum is eccentric and positioned on the margin except where the valve center is expanded. The striae on the rapheless valve are distinctly punctate and have the same density as on the raphe valve. The rapheless valve striae are mostly parallel, tending to convergent and curved near the apices. Areolae on both valves are coarse and distinct, 11-12 in 10 µm. As a result of the concave and convex valve faces, the girdle view of A. inflata gives a recurved shape where the raphe valve valve fasica is on the inside of the curve.