The ptyctodontids ("folded-teeth") are the monotypic order Ptyctodontida of unarmored placoderms, containing only the family Ptyctodontidae. With their big heads, big eyes, and long bodies, the ptyctodontids bore a superficial resemblance to modern day chimaeras (Holocephali). Their armor was reduced to a pattern of small plates around the head and neck. Like the extinct and related acanthothoracids, and the living and unrelated holocephalians, most of the ptyctodontids are thought to have lived near the sea bottom and preyed on shellfish.

The ptyctodontids ("folded-teeth") are the monotypic order Ptyctodontida of unarmored placoderms, containing only the family Ptyctodontidae. With their big heads, big eyes, and long bodies, the ptyctodontids bore a superficial resemblance to modern day chimaeras (Holocephali). Their armor was reduced to a pattern of small plates around the head and neck. Like the extinct and related acanthothoracids, and the living and unrelated holocephalians, most of the ptyctodontids are thought to have lived near the sea bottom and preyed on shellfish.