Phylogenetic analyses suggest that the tolypelepidid genera, including Athenaegis, Asketaspis, and in particular, Tolypelepis, are the sister-taxa of cyathaspidiforms.

Ctenaspidae encompasses the ctenaspids, (Ctenaspis, Arctictenaspis and Zaphoctenaspis), and the allocryptaspids (Boothiaspis, Allocryptaspis and Alainaspis).

All the cyathaspidiforms of Suborder Amphiaspidida, sometimes treated as a distinct order "Amphiaspidiformes," are endemic to Lower Devonian marine strata of what is now the Taimyr Peninsula, Siberia, in what was once a series of hypersaline lagoons cut off from the ocean.

In addition to having the plates of the cephalothorax armor fused together to form a muff-like unit shaped like a pot pie or a hot water bottle, all amphiaspidids had a simple, slit-shaped mouth, and reduced or no eyes.

These adaptations suggest that the living animals were filter- or suspension-feeders that habitually buried themselves in the substrate.