Cyathaspis is the type genus of the heterostracan order Cyathaspidiformes.^[1] 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]}