sand dollar

noun

1. any of various flat, disklike sea urchins, as Mellita testudinata or Echinarachnius parma, that live on sandy bottoms off the coasts of the U.S.

noun

1. any of various flattened disclike echinoderms of the order Clypeasteroida, of shallow North American coastal waters: class Echinoidea (sea urchins)