HOW SNAILS BUILD A SHELL

All they need is a specialised organ, some calcium-rich food and time

- WORDS SCOTT DUTFIELD

For more than 500 million years, marine snails have been growing their own homes, along with many other mollusc relatives. Around 150 million years ago, a clade of snails called Stylommatophora moved out of the ocean onto land, bringing their shells with them to form the world's terrestrial snails, also known as gastropods. And like their water-dwelling cousins, snails start forming their back-bound homes before they hatch.