metastome

from The Collaborative International Dictionary of English v.0.48

Metastoma \Me*tas"to*ma\, Metastome \Met"a*stome\, n. [NL.
   metastoma, from Gr. meta` behind + sto`ma mouth.] (Zool.)
   A median elevation behind the mouth in the arthropods.
   [1913 Webster]