Because the coiled shells of gastropods are asymmetric, they possess a quality called chirality–the "handedness" of an asymmetric structure.
Over 90% of gastropod species have shells in which the direction of the coil is dextral (right-handed). A small minority of species and genera have shells in which the coils are almost always sinistral (left-handed). Very few species show an even mixture of dextral and sinistral individuals (for example, Amphidromus perversus).