periostracum

noun

peri·​os·​tra·​cum

ˌperēˈästrəkəm

plural periostraca

-kə

: a chitinous layer covering the exterior of the shell in many mollusks, being usually well developed in freshwater forms, and serving to protect the shell from corrosion

Word History

Etymology

New Latin, from peri- + Greek ostrakon shell

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