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Any time you break a tooth, it means a painful trip to the dentist. For the sea urchin, it’s just part of the daily grind. As it chews through algae and rocks, the sea urchin’s teeth are designed to break off in a way that retains their cutting edge.
For humans, a broken tooth means a trip to the dentist. For sea urchins, a broken tooth reveals an incredible design.
Sea urchins are known for their long spines protruding from their shells. But these marine creatures hide many marvels under that menacing armor, including ball-and-socket joints connecting the spines, hundreds of adhesive tube feet, and a mouth containing five symmetrical teeth. Those teeth may one day help scientists develop tools and mechanical parts that never go dull.
Urchins need their sharp teeth not only to grind up algae but also to dig down into rock and create hiding holes. The mystery that has puzzled researchers is how these creatures are able to cut through rock with teeth made of calcite, which is relatively soft and not well suited for drilling. For more than a decade, scientists at the Weizmann Institute of Science in Rehovot, Israel, tried to uncover the secret.
The answer was in the details. Crystals of magnesium calcite, which is harder and denser than plain calcite, exist throughout the urchin’s teeth and are concentrated at the grinding tips. These harder crystals function much like sandpaper—the ragged surface slowly rubs away the rock.
Beyond this, the crystals that form the teeth are aligned into plates piled on top of each other. Two sets of these plates—set off by a few degrees—make up each tooth and are connected much like intertwined fingers. As the teeth wear down, the layers break off and expose new jagged edges so that they’re always ready to grind more rock.1
LiveScience.com rightly calls this marvel of engineering “smart structural design.”2 Although the writers likely mean evolution gave rise to these structures, the humble sea urchin teaches a very different lesson: God, the master Designer, provides a testimony to His ingenuity in even the smallest details.