nMetastoma(Zoöl) A median elevation behind the mouth in the arthropods.
Century Dictionary and Cyclopedia
nmetastomaIn Crustacea, a median development, often bifid, of the ventral part of a somite immediately behind the mouth. It is the so-called labium or under lip, composed of small pieces immediately below or behind the mouth. Also called hypostoma. See the quotation, and cut under cephalothorax.
Webster's Revised Unabridged Dictionary
NL. metastoma, from Gr. meta` behind + sto`ma mouth