Ramshorn snails, a group of freshwater snails, are easily to identifiable at a glance, because the shell is a flat, disklike coil, similar to a ram’s horn. 
Ramshorn snails are grouped with the lunged, or “pulmonate” snails, for they breathe air by means of a lunglike organ, and do not breathe water via gills.
Like other pulmonate snails, they lack an operculum, the hard horny “trapdoor” that other types of aquatic snails possess that closes when the animal retracts into the shell.
Adult shell diameter: from about 1/8 to 3/4 inch, can vary between species. 
Most ramshorn snails are herbivorous. Like many other snails, they have a radula, sometimes called a “rasping tongue,” that scrapes against the substrate they are crawling across.
Algae and other plant materials form the bulk of the diet.
Ramshorn snails make a great live food for puffer fish as well as aquatic turtles such as red eared sliders.