Cyathaspis is the type genus of the heterostracan order Cyathaspidiformes. Fossils are found in late Silurian strata in the Cunningham Creek Formation, New Brunswick, Canada and Europe, especially in the Downton Castle Sandstone of Great Britain and Gotland, Sweden.[citation needed] The living animal would have looked superficially like a tadpole, albeit covered in bony plates composed of the tissue aspidine, which is unique to heterostracan armor.[citation needed]

Cyathaspis ludensis is the earliest British vertebrate fossil.[citation needed] It was found in rocks at Leintwardine in Herefordshire, a noted fossil locality.[citation needed]