Ostracodermi

plural noun

Os·tra·co·der·mi

in some classifications : a suborder of the order Plectognathi comprising the boxfishes

in some classifications : an order or other category comprising the superclass Agnatha except the class Cyclostomi and some members of the class Placodermi that are known only from imperfect remains found in Ordovician, Silurian, and Devonian rocks, that lack jaws and limb girdles as well as paired fins homologous with those of recent fishes, that in most forms show the very broad anterior part of the body to be encased in a bony armor, and that have the slender scaly posterior part ending in an unsymmetrical tail