Gilled Aquatic Snails (Prosobranchs)

Family: 
In Missouri, 4 families in the former subclass Prosobranchia (gilled snails) in the class Gastropoda (snails, slugs)
Description: 

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. Prosobranch snails have a long incurrent siphon (tube) that draws water into the mantle (the tissue connecting the body to the shell), where gills extract oxygen. Thus they are able to “breathe” underwater much like a clam. Another key characteristic of prosobranch snails is the operculum, a hard, horny, rounded “trapdoor” attached to the foot that seals the opening when the animal retracts into the shell. It functions to protect the snail from predators as well as to keep it from drying out if it should be stranded out of water for a time.

Size: 
Shell length: ranges from 1/16 to 1 3/4 inches; most are around 1/2 to 3/4 inch (varies with species).
Habitat and conservation: 
Various species are found in all types of aquatic habitats, though in Missouri, the only region where gilled aquatic snails dominate is the Ozarks, where the many well-oxygenated, flowing streams and spring branches support these types of snails. Several Missouri gilled snails are cave species. As with other aquatic organisms, such as darters and minnows, the many separate, small streams of this region often support different species due to geographic isolation.
Foods: 
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.
Distribution in Missouri: 
Statewide, but most commonly encountered in the Ozarks. (In other Missouri aquatic regions, the pulmonate, or “lunged” snails tend to predominate.)
Status: 
Because many of our prosobranch species are limited to individual, separated watercourses, they tend to be less widespread and are more vulnerable to localized environmental disruptions. Nearly a dozen (or almost a half) of Missouri’s gilled snails are Species of Conservation Concern and are vulnerable to extirpation from our state. Four of these are cave snails. One species, the Tumbling Creek cavesnail (Antrobia culveri), is listed as in danger of extinction in Missouri and federally.
Life cycle: 
Most prosobranch snails have separate sexes; an individual is either male or female. Fertilization is usually internal, and freshwater prosobranchs typically lay eggs in clusters within gelatinous cocoons.
Human connections: 
Most people are intrigued by snails, and many think of snails symbolically as a representative of “slowness.” The shells of snails (especially those of some of the spectacular and colorful marine species) are prized by collectors, made into jewelry and other decorative objects.
Ecosystem connections: 
Aquatic snails play an intermediate role in aquatic food chains, eating plants and then becoming food for something larger. Several types of fishes have specialized throat teeth for cracking snail shells. Some birds and other animals eat snails, too.