Scientists explain blue stripes on tiny, near-invisible mollusk

Scientists at MIT and Harvard were recently able to detail the photonic structures embedded in the blue-rayed limpet's shell that give the species its signature shiny streaks.
The blue-rayed limpet is only the size of a fingernail. Its shell is almost entirely translucent. Hiding in the cold water kelp forests of Norway, Iceland, the United Kingdom, Portugal, and the Canary Islands, it's a wonder scientists were even able to find the species.
The tiny mollusk would be nearly impossible to detect -- whether by prey or inquisitive marine biologists -- if not for one small detail.
Unique dotted lines streak across the mollusk's tiny shell. When light bending through the ocean water hits the mollusk at just the right angle, the stripes beam back a brilliant fluorescent flash, giving away the limpet's presence in the seaweed beds.
But why, scientists wondered, and how?
Biologists suggest the mollusk's so-called rays are a way for the limpet to look more like a poisonous marine snail that occupies similar habitat. Simple enough. But, how?
How it creates these mimicking streaks is more complicated. Scientists were able to find out using optical microscopy, spectroscopy and diffraction microscopy to detail the nano-architecture of the inner portions of the mollusk's shell. Just beneath the thin layers of calcium carbonate that form the top and bottom of the shell lies a disorderly zigzag structure of rounder particles of calcium carbonate.
The zigzag pattern reflects the blue light while the layers underneath absorb it, creating the brilliant neon blue reflection.
Researchers say their new understanding of this internal design could have industrial and technological applications.
"Let's imagine a window surface in a car where you obviously want to see the outside world as you're driving, but where you also can overlay the real world with an augmented reality that could involve projecting a map and other useful information on the world that exists on the other side of the windshield," co-author Mathias Kolle, an assistant professor of mechanical engineering at MIT, explained in a press release. "We believe that the limpet's approach to displaying color patterns in a translucent shell could serve as a starting point for developing such displays."
The mollusk's internal optical structures are detailed in the latest issue of the journal Nature Communications.