The gastropods are the most diverse group of mollusks, and include snails, slugs, limpets, conchs, sea slugs, and others. They typically have a coiled body form with a twisted gut and nervous system. The coiling results in the unusual arrangement of their anus being above their head. Most have a corresponding coiled shell. Coils are added as the gastropod grows, and they tend to get larger, making a cone shape. Some shells are adorned with spines, grooves, or other textures that add strength. Many have a hard flap (operculum) on the foot that can be closed over the shell opening like a trap door. The shape of a gastropod shell often can be used to identify species. A gastropod's shell not only protects it from predation, but also keeps land species (terrestrial) from drying out. Some terrestrial gastropods that live in humid places, such as slugs, have a thin shell or no shell at all.

Most mollusks have a "radula", a ribbon made of chitin with rows of teeth (denticles). The radula is always used to feed, but how it is used varies widely. Radulas are specialized to the diets of mollusks, which range from fully carnivorous to entirely herbivorous. The radula may be used to filter, scrape, crush, cut, or stab, depending what food is eaten. Predatory murexes use the radula to drill holes into other mollusks, whereas limpets use it to scrape algae off rocks. The shape of the radula and denticles can be used to figure out what mollusk it came from. Nudibranchs that feed on corals have long, skinny denticles for scraping the thin layer of flesh off the coral skeleton. Queen conchs have a comb-like radula with thousands of tiny denticles for filtering small food from the water. Regardless, as denticles wear away, they are continuously replaced from top to bottom.