Galeaspida

Galeaspida ("Helmet shields") is an extinct taxon of jawless marine and freshwater fish. Their name is 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 is now Southern China, Tibet and Vietnam. Their morphology is superficially similar to that of the Heterostraci more than the Osteostraci, as there is currently no evidence that the galeaspids had paired fins. However, the Galeaspida are regarded as being more closely related to the Osteostraci than Heterostraci as the morphology of the braincase is more similar to that of Osteostraci than Heterostraci.