P Didymum Guide
Credit: Marina Potapova
  1. Valves small, less than 10 µm in length
  2. Valve outline linear-elliptical
  3. Central margin of valve constricted

Valves are linear-elliptical, slightly constricted in the middle. The raphe valve has a small circular or elliptical central area. The raphe is straight, without terminal fissures. The rapheless valve has a large rhomboid axial area. Striae are radiate on both valves and interrupted at the valve margin. Striae number 28-32 in 10 µm on raphe valve, 25-28 in 10 µm on rapheless valve .