Pliocaenicus Iconic
  1. Valve face transversely undulate
  2. Rows of areolae radiate from valve center
  3. Valve face with central fultoportulae

The valve face of Pliocaenicus has a distinct transverse undulation. Areolae radiate from the valve center in single rows, rather than being organized into groups, or fascicles. A number of fultoportulae are positioned at the center of valve face. Marginal fultoportulae are present between the striae, near the valve/mantle interface. Species in Pliocaenicus lack areolae on the valve mantle, below the marginal strutted process.

Pliocaenicus shares a number of features with Cyclotella, Cyclostephanos, and Stephanodiscus. Many of the distinguishing features are visible in SEM. This genus is known from oligotrophic lakes in Siberia, Mongolia, western North America and Pleistocene deposits in Alaska.