Definition of metastoma in English:
metastoma
(also metastome)
noun ˌmɛtəˈstəʊməmɪˈtastəmə
Zoology The labium of a crustacean.
Origin
Mid 19th century; earliest use found in Thomas Huxley (1825–1895), biologist and science educationist. From meta- + stoma.