rudist

noun

(paleontology) Any of many box-, tube- or ring-shaped marine heterodont bivalves from the Jurassic and Cretaceous periods.

The rudist is a type of fossilized marine organism.

意味（1）

(paleontology) Any of many box-, tube- or ring-shaped marine heterodont bivalves from the Jurassic and Cretaceous periods.

In its shallow waters, now-extinct clams known as rudists formed extensive beds.