Most people know a snail when they see one, but it is less common to be able to tell the difference between the two main types of aquatic snails. Instead of breathing underwater through gills, pulmonate snails breathe via a lunglike pulmonary cavity located within the mantle (the mantle is the part connecting the muscular foot and the head to the shell, and it secretes the material that forms the shell). Many pulmonate snails crawl to the water surface to take in air, but others can stay underwater all the time. Another, more obvious characteristic of pulmonate snails is that they lack an operculum, a hard horny “trapdoor” that other types of aquatic snails have that closes when the animal retracts into the shell.
Shell length: 1/8 to 1 inch; most are less than 1/2 inch (varies with species).
Statewide. Except for the Ozarks, pulmonate snails predominate in most of the aquatic regions in our state. (The prosobranch, or gilled snails, are most commonly encountered in the Ozarks, where waters are clearer, cooler, and have more dissolved oxygen.)
Habitat and Conservation
Various species are found in all types of aquatic habitats. Biologists understand that the first snails originated about 550 million years ago in saltwater, with some types later adapting to freshwater (via estuaries) and then to land. Pulmonate snails, with their “lungs,” are the group of snails that adapted to land and include our common garden snails and slugs. The freshwater pulmonate snails apparently represent descendants of land snails that readapted to lives in freshwater.
Most freshwater snails graze on plant material or (sometimes) scavenge on dead animals. It is common to see pond snails gliding about on submerged rocks; each one is scraping algae from the surface using a minute mouthpart called a radula, often described as a “rasping tongue.” If you collect pond water in a jar and place pond snails into it, you will soon be able to see these mouthparts as the snails attempt to forage on the glass.
Some of Missouri’s pulmonate snail species have been listed as Species of Conservation Concern, which means that they are vulnerable to becoming extirpated from our state. Two of these are the marsh pondsnail (Stagnicola elodes) and the Sampson sprite (Micromenetus sampsoni, also called Menetus sampsoni). As with most aquatic species, protecting their habitat, including water quality, is key to their survival.
Pulmonate pond snails are hermaphroditic, meaning that each individual functions as both female and male, and a pair of mating snails typically fertilize each other, with both individuals laying eggs afterward. Pulmonate snails typically lay gelatinous masses of eggs underwater on the surfaces of plants or rocks.
Aquatic pulmonate snails, globally, have many interactions with humans. They form an important link in aquatic food chains, from which humans glean fish for needed food. In many tropical countries, some types of pulmonate snails can be intermediate hosts for parasites that harm people.
Snails eat plant material, which becomes their flesh. They extract calcium from the water and convert it into their shells. Some sunfish specialize in eating snails, whose shells add calcium to their diet. The redear sunfish, for example, is called “shellcracker” for the heavy, pavement-like throat teeth it uses for crunching mollusks.