Mid Silurian to Early Devonian | image = Galeaspida_1.JPG | regnum = Animalia | phylum = Chordata | subphylum = Vertebrata | classis = Galeaspida }} Galeaspida ("Helmet shields")'s an extinct taxon of jawless marine and freshwater fish. Their name's derived from a latin word for helmet, galea, and refers to their massive bone shield on the head. Galeaspida lived in shallow, fresh water and marine environments during the Silurian and Devonian times (430 to 370 million years ago) of what's now Chi… (More on Galeaspida)