ostracoderm

noun
os·tra·co·derm | \ˈä-strə-kō-ˌdərm, ä-ˈstra-kə-\

Definition of ostracoderm 

: any of various primitive, extinct jawless fish (class Agnatha) of the Lower Paleozoic with a bony covering of plates or scales serving as a protective armor and which on the broad head usually form a bony shield of fused plates

Note: Distant relatives of the hagfish and lampreys, ostracoderms were typically less than 12 inches (30.5 centimeters) long. Unlike earlier vertebrates using the gills for both feeding and breathing, ostracoderms were the first known forms to use the gills exclusively for respiration.

First Known Use of ostracoderm

1890, in the meaning defined above

History and Etymology for ostracoderm

ultimately from Greek ostrakon + derma skin — more at derm-

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The first known use of ostracoderm was in 1890

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