Cycloptychius is an extinct genus of prehistoric freshwater & marine ray-finned fish that existed throughout much of the Carboniferous period in Eurasia, and possibly into the Early Permian in South Africa. It was a member of the Rhadinichthyidae, a family of basal ray-finned fish that was formerly placed in the now-paraphyletic order Palaeonisciformes.
It contains the following species: