Sand dollars are flat, burrowing sea urchins found on sandy ocean floors, primarily in shallow waters. They have a distinctive round shape and a light, often white or grayish color. The surface of a sand dollar is marked with five petal-like designs, which are actually the remnants of their feeding structures. When alive, sand dollars are covered in a velvety skin of tiny spines that help them move and feed on small particles. After they die, their skeletons, known as tests, wash ashore and can be found along beaches, often collected as souvenirs by beachgoers.