We brought home a new kitchen knife from my parents last month. The knife block was full, but Charlie exchanged the new one for what was previously our smallest and dullest. He wasted no time wrapping the old one up in plastic and hiding it from me. My hand naturally gravitates towards whichever tool will fit nicely inside it, even when I’m cutting a monster squash. We have a good arrangement: Charlie keeps the knives sharp, I keep my fingers, and I toss him the odd carrot slice in return.

But could he eventually be replaced by a sea urchin? A new study in the journal Advanced Functional Materials explains how sea urchin teeth never dull or break. In fact, they get sharper with use1.

Most people are probably familiar with sea urchins as the spiny little balls one occasionally encounters on the beach. Evil looking, but mostly harmless, so long as you avoid stepping on them. Sea urchins live in shallow tidal pools, eating algae and other plant material. So why do they need such sharp teeth? Much like their spines, the teeth probably serve a protective function. The urchins use them to chew burrows, often in solid rock, where they can take shelter from predators and waves.

In the current study, a group of physicists and biologists used an arsenal of sophisticated imaging, chemical and nano-scale stress test procedures to investigate the teeth of the California purple sea urchin (Strongylocentrotus purpuratus). Like starfish and sea cucumbers, urchins are members of a group of animals known for their penta-radial, or five-fold, symmetry. They have five teeth arranged in what is known as Aristotle’s lantern.

Aristotle's lantern

Aristotle’s lantern, as viewed from below with teeth closed. From Killian et al. 20111.

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