Why do seashells have patterns?
A Because they often go unseen, the elaborate patterns on mollusc shells remain one of nature’s mysteries. Cone snails, for example, have stunning shells, yet spend most of their lives burrowed in the seabed, only emerging at night. Plus, many shells have a hairy protein layer, known as the periostracum, which conceals their decorations.
Biologists used to think that patterns evolved at random and served no purpose. But one theory suggests they could serve as markers for shell-making. Molluscs grow their shells by secreting layers of calcium carbonate at the open end. They might use the patterns to line up their bodies and ensure the deposits are laid in the right place.