Photo: How Are Seashells Formed?

A zebra winkle shell on the beach

John Turnbull / Flickr

Our photo of the day provides a lesson in the origins of seashells. What a beautiful shot of a zebra winkle (Austrocochlea porcata) shell this is – it begs the question, where did it come from? How do sea creatures make their homes? Hermit crabs borrow the shells of others, but mollusks like snails, clams, oysters and others are responsible for building their own – which they do by secreting proteins and minerals from the mantle tissue that is located under the shell itself. Fancy trick, right? The shells have three distinct layers and are mostly calcium carbonate with just a dash of protein, and they grow from the bottom layer up by adding more to the margins. Since shells are not shed, they have to grow along with their inhabitants. For sea snails like the winkle here, that means the newest part is right at the opening which is constantly being added to from the mantle, resulting in beautiful homes for these cool critters. Photo by John Turnbull. Would you like to see your nature photo featured as the TreeHugger photo of the day? Join TreeHugger’s Reader Photo Pool on flickr and add your pictures to the group.