The inky depths of the ocean’s twilight zone harbor fist-sized shrimp-like crustaceans with ridiculously large eyes. Most cystisomeThe head is occupied by the eyes – all the better for being able to see in the dark. “The bigger you make your eye, the more likely you are to capture photons that are out there,” says Karen Osborn, a research scientist at the Smithsonian Institution in Washington DC.
The ocean is one of the last truly wild places on earth. It is teeming with fascinating species that sometimes border on the absurd, from fish that peer upwards through transparent heads to golden snails with iron shells. We know more about outer space than the deep oceans, and science is only just beginning to scratch the surface of the rich diversity of life below.
As mining companies push to industrialize the seabed and global leaders continue to bicker over how to protect the high seas, a new Guardian Seascape series will portray some of the weird, wonderful, majestic, ridiculous, tough and overwhelming creatures recently discovered. They show how much there is still to learn about the world’s least-known environment – and how much needs to be protected.
A major challenge for animals living in deep central water, in cystisomeThe fall between 200 and 900 meters depth can be seen without being seen by predators. “It’s basically like playing hide-and-seek on a soccer field,” says Osborn. “There’s nothing to duck behind.”
Eyes are particularly difficult to hide, as the retina must always contain dark, photon-absorbing pigments that predators can detect either in the dim illumination of the twilight zone or in the beams of their own bioluminescent searchlights. cystisome disguises its huge eyes in a unique way. Instead of concentrating the pigments in a small area, they spread their retinas into a thin layer of tiny reddish dots that are too small for most animals to see, Osborn says.
cystisome hides most of the rest of the body by being completely transparent. When scientists trawl them and dump them into a bucket of seawater, they appear as empty, palm-sized gaps between other animals. “You really can’t see these things until you pull them out of the water,” says Osborn.
Most cystisomeWomen’s internal organs appear crystal clear thanks to the very neat, structured arrangement of their tissues, Osborn explains. “The only thing they don’t seem to be very good at is gut feeling,” she says. The golden structure visible under the eyes is the digestive organ. This is also stacked high and straight to cast as small a shadow as possible cystisome hangs in its usual horizontal position.
These crustaceans are even harder to see underwater by reducing the light reflected off their transparent bodies, Osborn and colleagues discovered in 2016. Seen under an electron microscope, parts of cystisomeThe exoskeleton of is covered in tiny protuberances that Osborn likens to a deep-pile carpet. Other parts are covered with a single layer of spherical shapes, which scientists believe could be colonies of an unknown form of bacteria.
The nanoscopic shaggy carpet and spheres make it 100 times more likely for light to pass straight through Cystisoma, rather than reflecting into the eye of a passing predator. “It works in the same way as an anti-reflective coating on a camera lens,” says Osborn.
Related: Discovered in the depths: the “Elvis worms” that sparkle in the dark
cystisomeThe legs of , in particular, benefit from the anti-reflective high-pile covering and the ball-covered joints, because otherwise they would easily catch the light when flicking and fidgeting. “These guys are absolute masters of transparent mid-water camouflage.”
But what if the almost invisible cystisome do you really want to be found? These crustaceans need to mate in order to reproduce. One clue to how mates find each other lies in the male cystisomeThe large antennae of are covered with structures that detect chemicals in the surrounding water. “They actually smell each other,” says Osborn.