Despite their name, starfish are echinoderms, not fish. They breathe through structures on their hard, spiny skin rather than gills and move through the use of the rows of tube feet that line the bottom of each of their arms instead of swimming. The tube feet are also utilized for detecting smells and tastes, as well as for sweeping food into the mouths of primitive starfish species. Most of the more advanced varieties of the creatures, however, protrude their stomachs out of their mouths to surround prey. When the digestive enzymes secreted by the stomach liquefy the prey, the stomach and food mass are sucked back into the body of the starfish.