How to wind snail shells up the wrong way

Prod a snail embryo with fine glass rods and you can make its shell coil in the opposite direction to normal.

This gives an insight into how and when bodily symmetry is controlled through a mixture of genetic programming and physical forces. "The onset of left-right symmetry in vertebrates is still unknown, and our work may shed light on this," says Reiko Kuroda, who led the team at the University of Tokyo, Japan, that reversed snail "handedness".

Kuroda and her colleagues worked with a snail species whose cone and bodily symmetry can be either right or left-"handed", depending on the action of a gene in the mother snail called nodal.

By prodding embryos gently with glass rods at the eight-cell stage, they could reverse the genetically determined handedness of each snail.

From that point on, all the symmetry of the snail was completely reversed from what would be expected from its ancestors, including the bodily position of organs such as the heart or anus, and the direction of coiling in the conical shell.