There are few places to hide in the open ocean. Even in the “twilight zone”—the depths where sunlight gradually fades away—a mere silhouette can mean the difference between being a meal and finding one. But Cystisoma, a little-studied crustacean cousin of the sand flea, has a dazzling way to elude predators: It’s as clear as glass. Now researchers at Duke University and the Smithsonian have discovered how the solid creature manages to be so transparent—a finding that could lead to our very own invisibility cloak.
Cystisoma belong to a suborder of marine crustaceans called hyperiid amphipods, which live in every ocean, from just below the surface to right near the floor. The insect-like animals are masters of disguise and evolved dramatically different camouflage depending on the depth. Below 3,000 feet, where sunlight ends, the species are red or black. Transparent species such as Cystisoma tend to live between 30 and 1,000 feet, where the light is increasingly dim.
To get to the bottom of Cystisoma’s disappearing act, Duke marine biologist Laura Bagge and Karen Osborn, a Smithsonian zoologist, went hunting off the coasts of Mexico, California, Florida and Rhode Island. Trawling with nets and searching with deep-sea-diving robots, they captured specimens of the roach-like critters, which are about the size of a human hand. In the lab, the scientists studied small bits of the animal’s shell under an electron microscope. The analysis revealed minute spheres all over the shell, as well as “tiny, hair-like, nipply-looking things” growing out of it, says Bagge. When the researchers used a computer to study how such microscopic structures affect light, they found the coating canceled out 99.9 percent of the light reflections, much as the egg-crate foam walls in a recording studio absorb sound. Moths’ eyes have a similar anti-glare coating, but this is the first time scientists have seen it used for camouflage.
The curious spheres look like bacteria living on the shell surface, but they’re smaller than any bacteria we know of, says Bagge; the team is using DNA analysis to be sure. The finding could be useful either way. Engineers might be able to design similar structures to increase the transparency of glass and the absorption of solar panels, or even aid a kind of invisibility cloak that similarly distorts light. For her own research, Bagge wants to find out how being almost invisible affects the crustaceans’ social lives: “How does one clear animal find another to mate with?”