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peristomium

noun
peri·​sto·​mi·​um | \ˌperəˈstōmēəm\
plural peristomia\ -​ēə \

Definition of peristomium 

: peristome especially : the foremost true segment of an annelid worm usually bearing the mouth

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History and Etymology for peristomium

New Latin, from peri- + stom- + -ium

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