Nanofrustulum cataractum guide
  1. Axial area asymmetric
  2. Striae vary in length
  3. Spines spathulate
  4. Striae continue from valve face onto mantle
  5. Segmented girdle bands

Valves are nearly circular to asymmetric. The axial area is asymmetric and striae vary in length. Spathulate spines are present at the valve margin, on the costae. Striae continue from the valve face onto the mantle.