Eriptychiida

Eriptychiida is an extinct marine taxon of vertebrate in the group Pteraspidomorphi.

The order contains only one genus, Eriptychius, and fossilized specimens from this genus have been found in North America. The group contains only two documented species: Eriptychius americanus and Eriptychius orvigi.

The structure of the dentine of eriptychiids is in many respects closer to that of heterostracans that to that of astraspids. This is the only argument to place them as the closest relatives to heterostracans, among the Ordovician vertebrates. However, eriptychiids differ from all other pteraspidomorphs in having a massively calcified endoskeleton, pervaded by canals for blood vessels.