And so are shells! Snails have coiled shells, and most coil in the right-hand direction: if you look at the shell with its tip pointing up, the opening is on the right side. These are called dextral shells, in contrast to left-handed ones, called sinistral. It’s long been suspected that the coiling direction, also known as chirality, is determined by a single gene. This was confirmed recently by Japanese researchers Masanori Abe and Reiko Usuda. Using complex gene-editing technologies to induce mutations in the freshwater snail Lymnaea stagnalis, the researchers were able to change the coiling direction in normally dextral freshwater snails, so that the snails’ offspring coiled in a left-handed direction. Atypical left-handed snails have their genital organs reversed, which prevents them from successfully mating with normal, dextral partners. This is reversed in species of snails with a normally sinistral shell, such as the Lightning Whelk. The image shows a large and very rare, sinistral Junonia that had been, until recently, included in the Museum’s “Gifts from the Sea,” accompanied by a very large, dextral shell of the same species. The latter is still on display in that exhibit.
