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What Gives Shells Their Colors?

People's fascination with seashells results in part from their amazing shapes and colors. Marine mollusks are generally described as animals with soft, unsegmented bodies and protective shells, although some mollusks, such as squid, do not have shells. While your skeleton is inside your body, a mollusk's is outside its body. Both are basically made from calcium carbonate. You find mollusks with a wide variety of shell shapes and colors that have evolved to help mollusks survive. Mollusks' shell colors and shapes help them gather food, survive water turbulence, attract mates and provide protection from predators.

How Is Color Made in Shells?
- Each chemical element has a characteristic color based on the wavelength of light it emits. Color comes from trace elements the various animals tend to concentrate in their shells and differences in the way they form the calcium carbonate crystals that make up their shells. Shell color appears to be the result of hereditary and environmental factors. Snails, for example, have a special organ called the mantle, which takes dissolved minerals out of their environment and turns them into calcium carbonate crystals. Most snails also have pigment glands that produce color compounds at the same time the mantle secretes calcium, creating the patterns and colors seen in their shells.
Color As Protection
- Many species of mollusks make pigments that match their shells to their background. Camouflage occurs even in the dark of the deep sea. Bottom dwelling mollusks blend in with the bottom colors to make themselves less visible to predators. If the bottom is white, this might result in no pigment being made. Mollusks may want to look different from their neighbors, making it difficult for predators to search them out successfully. The coloring of some mollusk shells is designed to scare predators away or to make them visualize the mollusk as a predator of theirs.
Color Strengthens Shells
- Some mollusk species have few predators that use vision to find them. Many shells have color patterns inside the shell or where it can't be seen. Color has internal uses; it serves a strengthening function for shells. Color patterns strengthen by aligning with the spiral or lengthwise structure of shells. A stronger shell rather than a thicker shell makes moving around easier. This helps protect mollusks against predators, such as crabs. Strengthening by color also provides benefits on the inside of shells. Cherrystone clams have purple along the inside edge of the shell where predators attack. The pigment makes it harder to chip the shell.
Other Uses of Color
- Some mollusks use color for temperature regulation. In some environments, a light-colored shell helps prevent the mollusk from drying out by maintaining a lower temperature.

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