Austroptyctodus Campbellodus Chelyophorus Ctenurella Deinodus Destnoporella Eczematolepis Goniosteus Kimbryanodus Materpiscis Palaeomylus Ptyctodopsis Ptyctodus Rhamphodopsis Rhynchodus The ptyctodontids ("folded-teeth") are placoderms of the order Ptyctodontida, containing the family Ptyctodontidae.

Their armor was reduced to a pattern of small plates around the head and neck.

On account of their radically reduced armor, some paleontologists have suggested that the Ptyctodontida were not actually placoderms, but actual holocephalians, some primitive group of elasmobranch fish, or even were the ancestors of the holocephalians, including the chimaeras.

Thorough anatomical examinations of whole fossil specimens reveal that the profound similarities between these two groups are actually very superficial.

The Ptyctodontida were the only known group of placoderms that were recognizably sexually dimorphic, in that the males had hook-like growths on their pelvic fins that were analogous to the clasping organs found in male sharks, and chimaeras.