metastoma

Etymology
From +.

Noun

 * 1)  A median elevation behind the mouth in the arthropods.
 * 2)  A ventral single plate located in the opisthosoma of some non-arachnid chelicerates in the extinct genus  which is involved in feeding and manipulating food.
 * 3)   A structure found in some mosses and liverworts that covers the mouth of the capsule from which spores are released.