Definition of "metastoma"

(zoology) A median elevation behind the mouth in the arthropods.

(zoology) A ventral single plate located in the opisthosoma of some non-arachnid chelicerates in the extinct genus Houia which is involved in feeding and manipulating food.

(botany) A structure found in some mosses and liverworts that covers the mouth of the capsule from which spores are released.  examples