ostracoderm definition by American Heritage Dictionary
The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Any of several groups of extinct primitive jawless fishes of the Ordovician through the Devonian periods in North America and Europe, having bodies that were encased in an armor of bony plates.
Origin: Greek ostrakon, shell; see ost- in Indo-European roots + -derm.
ostracoderm - Science Definition
Any of three orders of small, 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).