Planorbidae

Planorbidae, common name the ramshorn snails or ram's horn snails, is a family of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks.

Many of the species in this family have coiled shells that are planispiral, in other words, the shells are more or less coiled flat, rather than having an elevated spire as is the case in most gastropod shells. Although they carry their shell in a way that makes it appear to be dextral, the shell of coiled planorbids is in fact sinistral in coiling, but is carried upside down, which makes it appear to be dextral.