Neidium Guide
Credit: Marina Potapova and Teofil Nakov
  1. Longitudinal lines evident
  2. Proximal raphe ends bilaterally deflected, or straight
  3. Striae uniseriate
  4. Apical flap often present

Neidium valves are linear to linear elliptical. Ends are variable in shape across species and may be rounded, capitate, rostrate or protracted. Longitudinal lines are present, formed by internal canals positioned along the valve margins. The proximal raphe ends are bilaterally deflected or straight. In many species, the distal raphe ends appear to bifurcate, forming an apical flap. Interruptions in the striae, or Voigt discontinuities, are frequently present in Neidium. Voigt discontinuities are positioned on the secondary side of the axial area along each raphe branch. The striae are uniseriate and composed of rounded, distinct areolae. Two plastids are present in living cells, positioned against the girdle.

Neidium is rarely abundant in collections, but the genus is broadly distributed. Neidium species often grow in slightly acid waters.