rudist
/ˈruːdɪst/(亦作rudistid /ruːˈdɪstɪd/)
noun
1- a cone-shaped fossil bivalve mollusc which formed colonies resembling reefs in the Cretaceous period厚壳蛤类（在白垩纪时期构成生物礁的一种锥形的化石双壳类软体动物）。
1.1
- Superfamily Rudistacea, order Hippuritoida.厚壳蛤总科, 马尾蛤目。
词源
late 19th cent.: from modern Latin Rudista (former group name), from Latin rudis 'rude'; for the variant spelling see -ID3.