Guide to Distrionella

Frustules of Distrionella are elongated with capitate ends. Valves may be slightly asymmetric to the transapical axis. Striae are unevenly spaced and become scattered and more irregular at the valve ends. Transapical ribs often evident. A central sternum is absent. Porefields, composed of simple porelli, are present at both valve ends. One rimoportula is present, and is usually positioned centrally within a stria near one pole.

Distrionella is distinguished from Diatoma by its more lightly silicified valves and weaker transapical ribs. It is considered to be closely related to Diatoma and Asterionella. Distrionella incognita is common in lakes and rivers of Montana and Idaho.