Nanoscale Structures Give Dragonfish Their Terrible, Invisible Teeth

Crystals in the enamel and an unusual interior structure render the giant teeth invisible, making the fish one of the deep seas’s most fearsome hunters

Audrey Velasco

The deep sea is dark and full of terrors, but perhaps the most terrifying creature of them all is the dragonfish, a jet-black critter with a jutting jaw full of knife-like teeth. But it’s unlikely that other creatures of the abyss even notice the mouth of ginormous chompers until it’s too late. That’s because the fish’s oversized teeth are transparent, making them invisible under water.

Now, a new study published in the journal Matter, has looked deeper into the structure of those unique teeth in one dragonfish species, Aristostomias scintillans, finding that the teeth are made of a material that may have applications beyond catching the dragonfish’s next meal.

Dragonfish are actually quite impressive: they may be less than a foot long and kind of slow, but they’re still the apex predator in their deep, dark layer of the ocean about 1,600 feet below the surface. Their jet-black bodies and see-through teeth keep them unnoticeable, unless illuminated by bioluminescent organs along their body and jaw. But many mysteries about the fish remain, including just what those stealth-mode teeth are made of.

“They spend most of their time sitting around with their jaws open, waiting for something to come by,” first author Audrey Velasco-Hogan, engineering graduate student at the University of California San Diego says in a press release. “Their teeth are always exposed, so it’s important that they are transparent so they don't reflect or scatter any bioluminescent light from the environment.”

To understand how the teeth work, Velasco-Hogan and an international collaboration of scientists looked at the nanostructure of the fish’s dentition using electron microscopy and other imaging techniques.

It turns out that dragonfish teeth are essentially a strange variation of conventional pearly whites. Like most chompers, the dragonfish’s teeth have two outer layers: an outer shell of enamel and an inner layer of dentin, which is normally composed of tubules connecting the enamel, the nerve cells and blood vessels in the center of the tooth.

But, reports Wudan Yan at The New York Times, the dragonfish enamel is studded with tiny crystals made of hydroxyapatite, just 5 to 20 nanometers in diameter. The crystals are structured in such a way that they prevent light from scattering off the teeth. The dentin is also unusual because it doesn’t contain microscale tubules, which scatter light making it visible, but is instead made of nanoscale rods of dentin. Essentially, the material isn’t super-exotic, but its structure is.

“Initially, we thought the teeth were made of another, unknown material. However, we discovered that they are made of the same materials as our human teeth: hydroxyapatite and collagen,” senior author Marc Meyers, also of UCSD, tells the Jeremy Rehm of the Associated Press. “However, their organization is significantly different from that of other fish and mammals. This was a surprise for us: same building blocks, different scales and hierarchies. Nature is amazing in its ingeniosity.”

At the microscale, the level at which most teeth are structured, light can interact and bounce off molecules leading to a nice bright white smile, Meyers tells Gizmodo’s Ed Cara. When structures are organized at the nanoscale level, however, light often just passes through without interacting.

“[W]hen the features of most any material are very, very small, light doesn’t scatter or bump off—it just goes through it,” says Meyers.

The biggest biological takeaway from the study is pretty obvious: the dragonfish likely evolved these unique stealth chompers to make them more effective predators. But the findings interest materials scientists as well. The nanostructures discovered could be used to develop new transparent materials, as materials scientist Chih-Hao Chang of North Carolina State University, who was not involved in the study, tells Yan.

“Biomimetics have provided many inspirations for engineers, and this is yet another great example,” he says. “It just goes to show how beautiful nature is all around us, and it can be really rewarding to take a closer look.”

Gizmodo’s Cara reports that team is now interested in learning how tough the dragonfish teeth are. If they’re strong, the research could lead to the development of a new type of rugged, transparent glass or ceramic.

And if the dragonfish teeth don’t pan out, there are more fish in the sea. The AP’s Rehm reports that the team is also interested in analyzing the chompers of other deep-sea fish with transparent teeth including anglerfish and hatchetfish.

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