Rhopalodia Guide
Credit: Ditmar Metzeltin, Marina, Potapova, Pat Kociolek
  1. Symmetry dorsiventral
  2. Raphe positioned in dorsal keel
  3. Valve faces nearly planar

Frustules of Rhopalodia have a strong dorsiventral symmetry. The raphe is positioned on the dorsal side of each valve in a shallow keel. The valve faces are nearly planar, that is, each frustule is shaped like 1/2 of an orange. The central endings of the raphe are expanded. The raphe is supported internally by costae. In contrast to Epithemia, Rhopalodia lacks complex cingula (girdle bands).

Cells of Rhopalodia grow in nitrogen poor habitats. Like Epithemia, cells typically include endosymbiotic cyanobacteria that fix atmospheric nitrogen.