Why are dragonfish teeth transparent?

Deep-sea dragonfish (Aristostomias scintillans) hide more than 500 meters under the sea, mouth open and a bioluminescent lure hanging on their chin. With proportionately large jaws, they can ingest prey by half their size, which helps them to maintain themselves for longer periods in the dark depths of the ocean, where food is scarce.

Dragonflies are predators in ambush and the key to their evolutionary success lies in the length of their teeth, their transparent teeth, which are actually invisible to prey that swim in low bioluminescence. The dragon dragon's jaw muscles are weak, but these saber-shaped teeth, shown here, are razor-sharp, to better perforate the prey when they close abruptly. (While piranha teeth have peaks of 14 μm in radius, those of dragonfish range from 2.5 to 5.0 μm.)

Materials scientist Marc Meyers and graduate student Audrey Velasco-Hogan of the University of California at San Diego are now collaborating with marine biologist Dimitri Deheyn and materials scientists Eduard Arzt, Marcus Koch and Birgit Nothdurft to understand what's on the cusp behind transparency. In a way, the dragon fish teeth look like those of other animals: they are composed of a layer of enamel coated with hard dentin. But in specimens collected off San Diego, the team used transmission electron microscopy and found details that distinguish the dragonfish. Nanocrystals of collagen and hydroxyapatite, of a width of about 1 nm and a length of up to 25 nm, are incorporated into the amorphous matrix of their stratum layer. # 39; enamel. Similar nanocrystals cover the dentin layer. In the team's optical spectroscopy experiments, the nanocrystals greatly reduced Rayleigh scattering of light from the teeth. The reduction acts as a camouflage. According to the team's badysis, the smaller the nanocrystal rays, the less effective they are as light diffusers. (A. Velasco-Hogan et al., material 1, 1, 2019.)