"ostracoderm." YourDictionary, n.d. Web. 05 December 2018. <https://www.yourdictionary.com/ostracoderm>.
ostracoderm. (n.d.). Retrieved December 05th, 2018, from https://www.yourdictionary.com/ostracoderm
Any of various extinct primitive jawless fishes of the Ordovician through the Devonian Period. Most ostracoderms had their heads or entire bodies encased in fused bony plates. Some or all ostracoderms are sometimes classified together with the modern cyclostomes (lampreys and hagfish).