This living jewel hides in plain sight.

Life in the twilight zone is a constant game of hide and seek. The crystal amphipod (Cystisoma spp.) combines invisible armor and giant eyes for a winning strategy.

Amphipods are shrimp-like crustaceans. Cystisoma is a deep-sea hyperiid amphipod. Most of their cousins grow no bigger than your fingernail, but the crystal amphipod can fill your entire hand. 

Cystisoma are also unusual because they swim freely in the open water. Many other hyperiids are hitchhikers, taking advantage of nearby jellies for food and shelter. Living out in the open requires the crystal amphipod to become almost completely transparent.

With the help of MBARI’s ships and deep-sea robots, our researchers and their collaborators revealed the secret to the crystal amphipod’s invisibility. Their exoskeleton is covered in microscopic shaggy structures or a fine coating of biofilm. Tiny spherical bacteria, only nanometers in diameter, work like the anti-reflective coating on eyeglasses to help Cystisoma camouflage in an environment that is sorely lacking in places to hide from hungry predators.

The crystal amphipod’s eyes are massive and cover up to a third of their body, helping them find transparent prey in the dim downwelling light. Their retinas are spread out into a thin sheet of tiny dots to reduce their shadow below.

Jellies are on the menu for the crystal amphipod. We have observed Cystisoma using those sharp pincers to tear bits of gelatinous tissue off a comb jelly.

Cystisoma mothers, like all amphipods, typically carry their babies within a special sac on their chest—even at the risk of blowing their invisible cover. Because her babies are reflective and visible to predators, mom does not brood her young for very long. She likely drops them off on a gelatinous host when they are quite small and leaves them to grow up on their own.

The crystal amphipod faces a fragile future. As industries look to the deep seafloor for mining precious metals, even animals living far above the bottom are at risk. Mining these metals will release plumes of dirty wastewater into the ocean’s twilight zone, clouding the crystal amphipod’s vision and interfering with their invisible superpower.

We urgently need to identify the impacts deep-sea mining will have on all ocean habitats, from the midwater to the seafloor. What we learn can help resource managers and policymakers guide decision-making about the ocean, its inhabitants, and its resources. Share what you have learned about the remarkable animals of the deep—together, we can be a powerful voice for the ocean.