Mary Esther Rice (August 3, 1926 – April 29, 2021) was an American invertebrate zoologist specializing in systematics, evolution and the development of marine invertebrates. She worked at the Smithsonian Institution as a curator, educator, research advisor, and administrator from 1966 until her retirement in 2002. She is known for her work on the life histories of Sipuncula, as well as for serving as the first director of the Smithsonian Marine Station at Fort Pierce.