A golden snail with a foot clad in iron weight seems like a creature from science fiction. But in a few remote places in the Indian Ocean, these snails are very real.
“It looks like an armored knight crawling around on the deep sea floor,” says Julia Sigwart, a biologist at the Senckenberg Research Institute in Frankfurt and one of the only people to have seen a live gastropod (Chrysomallon squamiferum)also known as a sea pangolin.
The snails’ habitat is extreme. They live several miles below the ocean’s surface on burning hydrothermal vents, which are bathed in toxic chemicals and can reach temperatures of more than 300C (572F).
The ocean is one of the world’s last truly wild spaces. It abounds with fascinating species that sometimes seem to border on the absurd, from fish that look up through transparent heads to golden snails with iron armor. We know more about deep space than deep oceans, and science is only beginning to scratch the surface of the rich diversity of life in the deep.
As mining companies push to industrialize the seabed and global leaders continue to wrangle over how to protect the high seas, a new Guardian Seascape series will profile some of the most recently discovered weird, wonderful, majestic, ridiculous, hardcore and sensational creatures. They reveal how much there is still to learn about the least known environment on Earth – and how much there is to protect.
The snails’ entire body and lifestyle revolves around bacteria growing inside a special bag in the throat, which converts chemicals that flow out of the valves into energy and thus provides all the snails’ food.
To keep the microbes well fed, bivalves developed enormous gills to absorb oxygen and chemicals from seawater, then deliver it through the bloodstream and an enormously spacious heart. A human heart of similar proportions would be the size of our heads.
When you say a species is endangered, everyone understands
Julia Sigwart, biologist
In 2019, researchers found that the scales on the snails’ feet are not to protect against predator attacks, but to ward off a poisonous threat that comes from within. The bacteria hidden in a scaly slug neck release sulfur as a waste product, which is fatal to slugs (it’s a common active ingredient in slug and snail killing pellets).
The internal structure of their shells act as tiny exhaust pipes, pulling the dangerous sulfur away from the snails’ soft tissues and depositing it as a harmless iron-based compound on the outside.
Although they developed many strange adaptations to survive on vents, gastropods did not settle on humans who showed interest in their habitat. All three sites where they live – an area of less than 0.025 square kilometers (0.01 sq mi), which together fit into St. Peter’s Square in Vatican City – are potential targets for deep-sea mining.
Mining companies are looking for gold, silver and other precious or rare metals deposited in the rocky walls of the black smokestacks. If their small areas of habitat are damaged or destroyed, the shell-footed snails will soon be gone.
Therefore, Sigwart and her team set about assessing the status of these rare animals and eventually had the gastropod snail added to the International Union for Conservation of Nature’s red list as an endangered species.
“It’s an incredibly powerful communication tool,” she says. “When you say a species is endangered, everyone in the world understands that.”
The bivalve was the first species in the world to be listed as endangered due to deep sea mining, but there are now many deep sea molluscs that experts have assessed and added to the global endangered list.
Related: Deep-sea mining could push hundreds of species to extinction, scientists warn
Of 184 endemic species that live only on valves, from giant clams to an obscure snail named after Joe Strummer from the Clash, only 25 are not considered to be in danger of extinction.
These species remain relatively safe, Sigwart explains, because they live in airfields where there is an explicit ban on any future development of deep-sea mining. This includes marine protected areas in the territorial waters of Canada and around the Azores.
Most of the other species live on hydrothermal vents out in the open ocean, which are outside territorial boundaries and therefore less protected and more open to mining exploration.
“These are the red list assessments that reflect the status and the risk to the entire species and its potential to actually go extinct and for us to lose it completely,” says Sigwart, “and nobody wants that.”
For Sigwart, these unusual molluscs brilliantly illustrate how evolution is about being good enough to get by. “It shows us the strange and convoluted paths life can take to adapt and survive,” she says.