An extinct jawless fish of the Cambrian to Devonian periods, having a heavily armored body.
- Class Agnatha: several orders.
- By the Middle Devonian the armoured jawless ostracoderms were in decline, and instead the jawed fish were undergoing a great evolutionary radiation in both the sea and in freshwater.
- With their armored head shield and trunk shield composed of overlapping bony plates, the placoderms appear at first glance extremely similar to the ostracoderms (armoured jawless fish).
- These were jawless, armored fish informally called ostracoderms, but more correctly placed in the taxon Pteraspidomorphi.
Late 19th century: from modern Latin Ostracodermi (former taxonomic name), from Greek ostrakon 'shell' + derma 'skin'.
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