The shell’s outer layer is not calcified at all, but is a thick layer of protein. The shell’s middle layer includes different proteins that lead to the formation of calcite instead, which is why it looks different than the inner layer. Its proteins cause the calcium carbonate to form fibrous aragonite crystals. The innermost layer is the layer that directly touches the mantle. There is a smooth and shiny inner layer, a chalky middle layer and a rough outer layer. “Generally one can think of growing shells as growing tubes,” said Chris Meyer, research zoologist and curator of mollusks at the museum.Įach mollusk’s shell contains three distinct layers – all made of the same material but arranged in different structures. They do this by building their shells little by little from their margins, like a tree creating new rings. Mollusks never shed their shells, so the creatures must increase their shell’s size as they grow. Cells in the mantle secrete all the proteins, chitin, and minerals necessary to create the shell. How do these squishy creatures construct their strong shells? It all starts in the mantle, the thin layer of flesh connecting a mollusk to its shell. Many sea snails fashion swirling shells, like this emperor's slit shell, that are decorated with intricate patterning. For instance, mother of pearl – the innermost layer of some seashells – is well known for being far sturdier than its carbonate component alone. “This makes seashells very special because composite materials have unique material properties,” said Gabriela Farfan, the museum’s curator of gems and minerals, who specializes in studying carbonates.įarfan explained how composite materials like seashells behave differently than their pure components. When present in seashells, the carbonates take on the crystalline form of either calcite or aragonite, depending on the shell type. The mineral component of shells is calcium carbonate – the same material eggshells are made of. The biological aspects include protein and chitin – the same material found in the shell of a crustacean like a lobster – and they form the flexible scaffold that minerals fill the gaps of. In the case of seashells, they are made of both mineral and biological features. Shells are actually part of a category of objects called “composite materials,” meaning they are composed of a combination of different components. While they may look like bumpy bones or sculpted stones, they are neither. Which begs the question - what are these sturdy shells made of? As the name suggests, all mollusks have soft, squishy bodies, so many species create firm shells for structure and protection. The word mollusk originates in part from the Latin word “mollis,” meaning soft. Most seashells come from a group of animals called mollusks, which includes everything from oysters to octopuses. Known for their vibrant patterns and glossy appearance, tiger cowry shells are found from the eastern coast of Africa all the way to Hawaii. As a result, seashells are useful to both aquatic critters and scientists on dry land – including those at the National Museum of Natural History. Constructed by everything from sea snails to scallops, seashells are beautiful biological treasures that contain hints of the marine environments they came from. Due to their varied charm, humans have prized seashells for as long as they have collected pretty things.īut by the time they wash ashore, seashells have already had an extensive history. From smooth to rough, spiraled to dished, and pure white to vibrant colors of the rainbow, shells come in all shapes, sizes, and textures. Seashells, often found lining the seashore, stand out among the sand like precious gems. With summer finally here, many of us are ready to hit the beach to beat the heat – which means it’s officially time to look for seashells. Not only is this regal murex seasnail shell stunning in appearance, but the stark contrast between the inner and outer shell highlights the complexity of seashell formation.
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