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periostracum

(per′ē äs′trə kəm)

a horny covering, secreted as the outermost layer of most mollusk shells, that protects the underlying shell from erosion

Origin: ModL < Gr peri-, around (see peri-) + ostrakon, a shell: see ostracize

See periostracum in American Heritage Dictionary 4

noun pl. per·i·os·tra·ca (-kə)

The hard chitinous outer covering of the shell of many mollusks, especially freshwater ones, that protects the shell from the erosive action of water.

Origin:

Origin: New Latin

Origin: : peri-

Origin: + Greek ostrakon, shell; see ost- in Indo-European roots

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