Continue reading...

Hundreds to thousands of feet below the surface of the ocean, beyond where sunlight can reach, another world exists. It’s called the twilight zone and the animals here vary from microscopic to very large. This cold and dark place is still somewhat of a mystery to scientists, where fascinating creatures unlike any others on Earth can be found. In these murky depths lives a creature that can make itself invisible.
The glass squid from the family Cranchiidae is nearly transparent with the exception of a few body parts, such as its eyes. When predators look down from below, they are searching the water for tell-tale shadows to help them locate prey. But the transparent body of the glass squid creates no shadow. To stop the eyes from casting shadows and revealing its location, special organs just below the eyes emit a bioluminescent glow. It’s a specialized camouflage technique that makes the squid nearly invisible to predators and prey. Watch the video above filmed by the Monterey Bay Aquarium Research Institute (MBARI) to see this amazing creature in action.

Glass squids have special pigment-filled cells, called chromatophores, that help them hide to evade predators.
©Edie Widder / Public domain / Wikimedia Commons – Original / License
How the Glass Squid Uses Its Chromatophores to Become Invisible
Glass squids have tiny pigment-filled sacs, called chromatophores, that cover their entire body. These are pigment-changing skin cells, and it’s the same thing octopuses use to change color. When the glass squid keeps the sacs closed, its body is see-through, making it invisible to predators and prey. The sacs look like tiny polka dots covering its translucent body.
However, if the glass squid is spotted, it can quickly fill up its chromatophores, darkening its entire body. It will then squirt ink and swim away to safety, relatively unseen through the dark depths. The glass squid can also squirt ink into its body cavity. Scientists think this may make them even darker in the dim waters, or it may serve as a chemical deterrent to creatures trying to eat it.
How Exactly Do Chromatophores Work?
In the center of each chromatophore is a tiny sac of pigment. The squid’s nerves and muscles control whether the sac is expanded or contracted. When it expands, it’s like a balloon filling up with a colored liquid. When all of the chromatophores across the squid’s body fill with liquid, the squid appears to be a different color. While most of the time the squid is nearly invisible with its see-through body, once it’s spotted, it can darken the surface of its body and disappear into the dark waters. A jet of black squid ink helps to further confuse its predators.
Why Glass Squids Need This Sophisticated Camouflage System
In the murky ocean twilight zone, also known as the mesopelagic zone, there are no places to hide. There are no plants because there isn’t light for photosynthesis, so animals can’t dart underneath vegetation for shelter, or hide among seaweed. The only way to escape being someone’s next meal is to hide in the dark.
The glass squid has no outer shell protecting its soft body. Its transparent skin, bioluminescence around its eyes, and the ability to darken itself are the only ways it can hide from danger, such as a sperm whale venturing into the twilight zone for a quick bite to eat.
Other Strange Facts About the Glass Squid
This intriguing creature has a few other fascinating traits that help it survive the strange environment it calls home. For one thing, it fills its empty internal cavity with ammonium. Because this chemical is lighter than water, it helps the squid to swim with less effort.
There are 60 different species of glass squid in the Cranchiidae family and they live in the deep water all around the world. Some of them, like the Cranchia scabra, are as small as four inches. While others, such as the colossal squid are massive. We don’t know much about the colossal squid because they are hard to spot. The colossal squid (Mesonychoteuthis hamiltoni) is the largest squid in the world, growing 33 feet long and weighing 1,000 pounds.
According to scientists at MBARI, we have more insight into the smaller squids because they are easier to film. The larger ones are such fast swimmers our slow-moving submarines can’t catch up to film them.
Why Scientists Are Racing to Learn All They Can About the Ocean’s Twilight Zone Creatures
Hidden deep in the ocean floor are nodules of precious materials such as cobalt, copper, manganese, iron, and other rare materials. These materials are used to build items such as cell phones, electric vehicles, and ion batteries. Companies are interested in finding ways to extract these materials from the ocean floor. And although commercial deep-sea mining isn’t happening yet, it may not be far off.
Scientists need further research on exactly how deep sea mining would impact the animals living in the twilight zone. Like the glass squid, many of these creatures rely on their eyesight and hearing to get around. They also communicate using bioluminescence. Mining the ocean floor would cause a lot of underwater noise and a release of wastewater plumes, clouding the water. Researchers don’t know yet how severely this could impact the animals living in this mysterious place. Nor do we fully understand the impacts it may have on the entire ocean ecosystem or Earth’s environment.
Thank you for reading! Have some feedback for us?
Contact the AZ Animals editorial team
Thank you for your feedback!
We appreciate your help in improving our content.
Our editorial team will review your suggestions and make any necessary updates.
There was an error submitting your feedback. Please try again.