Pfitzer 1871      Category: Symmetrical biraphid
TYPE SPECIES: Neidium affine (Ehrenberg) Pfitzer




Smallest to largest - 4 taxa sorted by maximum length

Image Credit: Marina Potapova and Teofil Nakov

CLASS: Bacillariophyceae
  ORDER: Naviculales
    FAMILY: Neidiaceae

  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.

Cite This Page:
Spaulding, S., and Edlund, M. (2008). Neidium. In Diatoms of the United States. Retrieved April 18, 2018, from

Contributor: Sarah Spaulding | Mark Edlund - December 2008
Reviewer: Sam Rushforth - June 2010