It lived during the Arenig stage of the Ordovician Period , approximately 478 to 471 million years ago .
Etheridgaspis is an extinct genus from a well - known class of fossil marine arthropods , the trilobites .
Etheridgaspis lived during the Arenig stage of the Ordovician Period , approximately 478 to 471 million years ago .
Etheridgaspis is an extinct genus from a well - known class of fossil marine arthropods , the trilobites .