periostracum

noun peri·os·tra·cum \ˌperēˈästrəkəm\

Definition of periostracum

plural

periostraca

\-kə\
  1. :  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

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Origin and Etymology of periostracum

New Latin, from peri- + Greek ostrakon shell — more at oyster


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