Pteraspidiformes is an extinct order of heterostracan agnathan vertebrates known from extensive fossil remains primarily from Early Devonian strata of Europe and North America, and from Upper Silurian Canada.

[1] Delicate, finger-like components of the anterior end of the ventral plate forming the edges of the mouth suggest that pteraspidiform heterostracans were filter-feeders that selectively filtered specific sized plankton from the water column.

Pteraspididae is an Early Devonian-aged family that contains the stereotypical, torpedo-shaped pteraspidids, such as the type genus, Pteraspis, and its close relatives Errivaspis and Rhinopteraspis, that are popularly thought to have actively swam about in the water column.

Species of Gigantaspis superficially resemble some genera of its sister taxon, Protaspididae, i.e., that they had armor shaped like a hot bun or a round loaf of bread.

Protaspididae is a family of bun or bread loaf-shaped pteraspidids found in Early Devonian marine strata from the Rocky Mountains of the United States, and of Europe.