On the underside of a sand dollar, there is a star pattern spreading out from the center where the mouth is. This star pattern is made up of that are called "food grooves". Sand dollars filter sand and water, catching plankton and other things on their spines. Then, with cilia, the spines move the food into a food groove, and the food travels down the food groove to the mouth. Its food consists of crustacean larvae, small copepods, diatoms, algae and detritus.