Sand dollars are flat, burrowing sea urchins found on sandy ocean floors. 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. These creatures are part of the Echinoidea class, which also includes sea urchins and sea cucumbers. Sand dollars primarily feed on tiny particles, such as plankton and organic matter, by using their tube feet to collect food from the sand. When alive, they are covered in a velvety skin, but they become hard and brittle when they die.