, a species of sea snail (now extinct) found mainly in the Northern Hemisphere.Right: The normally dextral (right-handed) shell of Neptunea despecta'', a similar species found mainly in the Southern Hemisphere.
Gastropods 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).
Flatfish , like other
flatfish, experience an eye migration during their lifetime, making them asymmetric. The most obvious characteristic of
flatfish, other than their flatness, is their asymmetric morphology: both eyes are on the same side of the head in the adult fish. In some families of flatfish, the eyes are always on the right side of the body (
dextral or right-eyed flatfish), and in others, they are always on the left (
sinistral or left-eyed flatfish). Primitive
spiny turbots include equal numbers of right- and left-sided individuals, and are generally more symmetric than other families. ==Geology==