Eugeneodontida

The Eugeneodontida are an extinct and poorly known order of bizarre cartilaginous fishes. They possessed a unique "tooth-whorl" on the symphysis of the lower jaw and pectoral fins supported by long radials. The palatoquadrate was either fused to the skull or reduced. Now determined to be within the Holocephali, their closest living relatives are ratfish. The meaning of the name Eugeneodont correlates to "true origin teeth", and comes from the Greek eu (good/true), geneos (race, kind, origin), and odon (tooth).

Members of the Eugeneodontida are further classified into different families, the most well-preserved members that have been discovered are commonly placed within the families Helicoprionidae ("spiral saws"), and Edestidae ("those which devour"), the former containing the genera Helicoprion, Sarcoprion, and Parahelicoprion, and the latter containing the genera Edestus, Listracanthus, and Metaxyacanthus. All eugeneodonts are thought to be obligate carnivores, with each genus having specialized feeding behaviors, territory ranges, and specific prey.