shell shell gastropod shell shell shell shell shell shell shape of the shell shell shell shell shell shell shell parietal callus shell shell shell shell Shells shell gastropod shells shell spire shell shell shell shell shell shell shells outer lip snail shell shell shell shell shell shell shell shell shell http://en.wikipedia.org/wiki/Gastropod_shell snail shell shells shell English outer lip shell aperture outer lip shell|shell shell shells shell shell shell shell gastropod shell gastropod shell shell shell shells shell shell shell shells shell coils Shells gastropod shells shell columella shell English shell shell apex spire snail shell shell shell shell shell shell shell shell shell shell shell shell shell shell shell shell shell shell columella shell shell shell shell shell snail shell shell shell shell shell shell English shell English shell snail shell shell shell shell shell shell shell shell shell English shell shell shell the spirals that they generate shells shell shell sinistral shells aperture shell outer lip outer lip shell shell shell gastropod shells Gastropod shell shell Gastropod shell § Chirality in gastropods shells shell shell shell shells shell spire