Gyrosigma Acuminatum Guide
  1. Valves slender, sigmoid
  2. Central area longitudinally elliptical
  3. Transverse and longitudinal striae equally distinct

Valves are slender and sigmoid, with a longitudinally elliptic central area. The distal raphe is slightly eccentric, positioned closer to the convex side. Proximal raphe ends are curved in opposite directions. The central transverse striae are slightly radiate, outside of the central part of the valve the transverse striae are parallel. Transverse and longitudinal striae are equally spaced.