Neptune's cup
/ˈnɛptjuːnz kʌp/ /ˈnɛptʃuːnz kʌp/noun
A marine leuconoid sponge of the genus Poterion, which forms a very large, goblet-shaped structure.
Origin
Mid 19th century; earliest use found in Robert Edmond Grant (1793–1874), comparative anatomist and transmutationist. From the genitive of Neptune + cup.