Subclass †Heterostraci Lankester, 1868 Family †Cyathaspididae Kiaer, 1932, nom. praeval. Subfamily †Cyathaspidinae [paraphyletic] Genus †Pionaspis Denison, 1964 †Pionaspis acuticostata Elliott, Lassiter & Blieck, 2021, orth. inval. see Pionaspis acuticosta Denison, 1964