scyphistoma
noun
scy·phis·to·ma sī-ˈfi-stə-mə 
plural scyphistomae sī-ˈfi-stə-(ˌ)mē also scyphistomas
also scyphistomas : a sexually produced scyphozoan larva that ultimately repeatedly constricts transversely to form free-swimming medusae
Word History
Etymology
New Latin, from Latin scyphus cup + Greek stoma mouth — more at stomach entry 1
First Known Use
1861, in the meaning defined above