Frustulia Kreubergensis Guide
Credit: Carrie Graeff
  1. Longitudinal ribs absent
  2. External proximal raphe ends unilaterally deflected
  3. Poroids near distal raphe ends
  4. Helictoglossae prominent

Unlike other species of Frustulia, F. creuzburgensis lacks internal longitudinal ribs. The external proximal raphe ends are unilaterally deflected, while the distal raphe ends are straight. The distal raphe ends terminate in a transverse depression that contains poroids. The helictoglossae are prominent in LM.