Nearly two miles beneath the surface of the Indian Ocean, a hydrothermal vent releases sulfur into the dark waters. On its edge, a small snail not only survives in this toxic environment but also transforms the poison into a shell partially made of iron. This remarkable creature is the scaly-foot snail (Chrysomallon squamiferum), considered one of the most metal animals on Earth.
Although this species is incredibly tough, its future is uncertain. In 2019, it became the first hydrothermal vent-dwelling species to be listed as endangered by the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species, primarily due to the looming threat of deep-sea mining companies targeting the minerals found at these vents, which the snails inhabit.
Initially, scientists believed the extreme pressure and toxic chemicals emitted from Earth’s crust through hydrothermal vents would make these environments inhospitable to life. However, in 2001, researchers discovered the snails thriving alongside numerous other species in these harsh conditions. The iron-rich shell of the snails plays a crucial role in their survival—not as armor, but rather similar to how a human liver functions by detoxifying the body, explains Chong Chen, a senior scientist at the Japan Agency for Marine-Earth Science and Technology and an expert on the scaly-foot snail. Chen led the genome mapping of the snail.
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The key to the snail’s survival lies in its unique way of obtaining nutrients. Unlike typical creatures, it does not consume food conventionally. Instead, it houses bacteria that feed on hydrogen sulfide, oxygen, and carbon dioxide, converting these chemicals into sugar. In return for providing a habitat for the bacteria in its gut, the snail utilizes this sugar for energy. However, the bacteria’s digestion process produces toxic sulfur as a by-product. To safeguard itself, the snail expels the sulfur, which then combines with the iron in the vent water, resulting in a shell that is partially metallic and features the tough scales from which the snail derives its name.
“The ‘iron armor’ is not for defense, as people thought for many years; instead it is for symbiosis. The snail is totally happy without the iron armor, which is a by-product formed by the hot vent environment,” Chen says.
Despite its small size of less than two inches, the snail has inspired technological advancements. The U.S. Army, for instance, has studied the snail’s scales to develop new armor, and its chemical makeup has led to innovations in creating pyrite nanoparticles used in solar panels.
This snail is the only known animal to incorporate iron sulfide into its shell and is found exclusively at eight sulfur-rich hydrothermal vents worldwide. The total area they inhabit is scarcely half the size of Disney World, according to Jon Copley, a marine biologist at the University of Southampton in England.
The very environment that facilitated the snail’s unique adaptation now threatens its existence. Hydrothermal vents form at the boundaries of Earth’s tectonic plates, where seawater penetrates the crust, gets heated by underlying magma, and rises back up, carrying valuable minerals like copper, zinc, and gold, along with the iron and sulfur present in the snail’s shell.
These minerals have attracted the interest of mining companies, particularly copper, which is in high demand for artificial intelligence data centers and green energy production. Although no deep-sea mining has commenced in these regions, at least two of the snail’s habitats are under consideration for potential operations, as noted by the IUCN.
“There are rising concerns that if mining is permitted, the habitat could be severely reduced or destroyed,” the organization wrote in its Red List entry. The best way to protect the vents—and the snails—is to “just not mine active hydrothermal vents, period,” Chen says.
Chen suggests that mining companies focus on inactive vents instead. “There are, for example, many inactive hydrothermal massive sulfide deposits in the Indian Ocean. These inactive vents no longer host the scaly-foot snail, and therefore mining these sites would not impact the snails,” he says. However, Chen cautions that inactive vents are not a perfect solution. “We currently know very little about how unique the inactive vents themselves are in terms of biodiversity,” he says. “Ongoing research has found at least some animal groups that seem to be unique to inactive vents, so mining there might impact those animals.”
Beyond the snail’s contributions to modern technology, Copley emphasizes the philosophical importance of preserving a creature that inhabits an environment as alien and remote to humans as any on Earth. While few will ever encounter a scaly-foot gastropod, this does not diminish its value.
Chen takes a more practical view. Although the snail itself may not directly affect humans, its ecosystem plays a more significant role in ocean health than previously understood. The vents circulate carbon and nutrients into the water, supporting the beauty and sustenance humans enjoy.
“We are now starting to understand that hydrothermal vents play key roles in regulating the supply of such elements to the ocean and therefore contributing significantly to the global biogeochemical cycles that we all rely on,” Chen says. “The world is one connected planet, more than one might realize. We are now living in the consequences of deforestation’s impacts on the climate, which we did not realize when it began. Mining hot spots like hydrothermal vents may lead to a similar impact.”
