Gyrosigma Obscurum Guide
Credit: Meredith Tyree
  1. Raphe strongly sigmoid
  2. Raphe eccentric near apices
  3. Transverse striae parallel
  4. Central area at oblique angle to margin

Valves are linear-lanceolate, with a strongly sigmoid raphe. The transverse striae are very fine (28-29 in 10 μm), parallel and evenly spaced throughout. Longitudinal striae are not evident. The central area is small and elliptic, and set at an oblique angle to the valve margin.