 They are often grouped together with the Arandaspidida.Astraspids are characterized by a dermal ornamentation of large, mushroom shaped tubercles of fine-tubuled dentine ("astraspidine"), covered with a thick, glassy cap of enameloid.Astraspids and eriptychiids were the first Ordovician vertebrates ever discovered in the 19th century, and they have long been the only known Ordovician vertebrates, until the discovery of the arandaspids, in the 1970s.