Mollusks are grouped onto three classes. Gastropods include snails, slugs, limpets, and conches. Gastro means “stomach.” Pod means “foot.” A gastropod’s foot is located under its body. All gastropods except slugs have a single shell. When danger threatens, these mollusks can pull completely into their shell. Gastropods have tiny teeth that rip up the plants or animals they eat. Some scrape algae off rocks for food.