Hermadion is a genus of marine polychaete worms belonging to the family Polynoidae, the scaleworms.

The elytra are large but leave a small median part of the body uncovered.

The prostomium is bilobed and rounded anteriorly, lacking acute cephalic peaks.

The neuropodial lobe is elongate and tapering to a narrow tip.

The notochaetae have pointed tips and are distinctly thicker than the neurochaetae.