Happy Halloween…month! Yes, much like in the rest of American culture, Halloween lasts through the whole month of October here at Consider Nature, and today we will be discussing a particularly-creepy creature. In addition to this article, I will also be doing a second article this month on another, equally-spooky creature. Look for that article closer to October 31st. This article is Halloween-themed, so it's going to be a little spooky. Content warning for drowning, suffocation, and thalassophobia.
Plenty of animals scare people: spiders, snakes, rats, dogs. Yet, plenty of us can pick up a huntsman spider the size of a dinner plate or an anaconda longer than a school bus with no problem whatsoever. Hell, some weirdos on Tumblr even think that spiders are cute. Is there something that everyone is afraid of, though, a situation that could cause even the most fearless person imaginable to panic? According to Michael Stevens, host of YouTube’s Mindfield, there is. In a laboratory setting, elevated levels of carbon dioxide in the bloodstream, provided that it is coupled with an obvious external threat, can elicit a fear response regardless of a person’s innate fears. These tests have even been able to incite fear in people with damage to the regions of their brain responsible for creating a fear response. Normally, these people cannot feel fear at all, yet when they inhale concentrated carbon dioxide, they feel absolute terror. The external threat in question can range from waterboarding to strangulation to…
Drowning.
You are falling deep into the sea, pulled deeper and deeper by something you cannot see. As you sink beneath the relentless waves, cold green sunlight filtering through the rippling water above, you kick, scratch, claw at the water, desperate to save yourself from certain death. You open your mouth to scream, and icy cold water rushes in, making your lungs burn like hot coals. Powerless to save yourself, you watch in horror as the light above grows dimmer and dimmer as the column of water between you and the surface grows insurmountable. You feel the water pushing on you from all directions, squeezing your body, collapsing your lung cavity and then expanding it to refill your lungs with fresh ice water. Your vision goes foggy. Your brain tunes to radio static. And the last thing you see before you die is the last light of the sun being swallowed by the sea, submerging your body in a fathomless black.
In this most-terrifying of places lives a creature utterly alien to our understanding of life. It lives exclusively in the infinite darkness, bracing cold, and crushing pressure of the deepest parts of the ocean. Where most animals would meet certain, inescapable death, this creature thrives, using adaptations that no other creature on Earth possesses to eke out an existence at the very edge of what is possible. Consider: the scaly-foot snail. Chrysomallon squamiferum.
Just look at that little monster! Terrifying, right? Scaly-foot snails are, as the name suggests, gastropods, just like any slug or snail you would find in your garden. They measure 35-45 millimeters in diameter (1.3 - 1.8 inches in Hamburger-speake), making them a little larger than a golf ball. Their bodies are pink and fleshy, while their vaguely spherical shells are solid black with brown bands. They have no eyes, and instead have facial tentacles which allow them to sense their environment. Like all snails, scaly-foot snails have a foot, a fleshy appendage that supports the snail and helps to move it around like a giant, mucus-covered magic carpet. This foot is unique amongst snails, though, in that it is covered in 5 mm long scales that look almost like feathers (or like the plates of a Roman Lorica Squamata for those history nerds out there). These scales act to defend the snail’s foot from damage, as unlike many snails, this species cannot pull their bodies fully inside of their shells. Most snails have a structure called an operculum which acts like a trap door, allowing them to pull inside of their shells and literally close the door behind them. Scaly-foot snails do have operculums, but they are very small and useless, just hanging out on the back of their shells like the tag on a very slimy tee shirt. As such, they armor their feet with socks that would fit right in at a Cannibal Corpse concert.
In the process of building their scales and shells, these snails do something that no other animal on Earth is capable of—they reinforce their armor with iron. Essentially, the snails absorb iron sulfide compounds from the water around them and use them to build an extra protective layer on top of their shells. Most molluscs (snails, clams, oysters, etc), have shells made of calcium carbonate. This is the same white, chalky material that makes up limestone, the internal skeleton of corals, and that gross-looking limescale on your bathroom sink. In most snails, this shell is then covered in a layer of proteins called the periostracum, which act as a scaffolding for the shell to continue growing thicker and help waterproof the shell. While calcium carbonate can be used to form very durable shells, many predators, such as crabs, are capable of breaking them with their powerful claws. The crab can do this by either crushing the shell directly or by wedging its claw up into the operculum and prying the shell open crowbar-like.
No crab in their wildest dreams would dare try to break a scaly-foot snail's shell, though. Scaly-foot snails have the calcium carbonate shells of a normal snail, but add two additional layers which make their shells nearly impenetrable. Above the calcium carbonate is a thick layer of protein and other organic substances, like an extra-thick periostracum, and atop that is their signature iron armor. This iron exterior is extremely hard, and the middle organic layer helps to dissipate kinetic energy, preventing the shell from cracking. This system makes the shells capable of withstanding even the most powerful attacks from predators in their habitats, and is even being studied by human materials scientists to create armor for people. The iron-reinforced shells are significantly harder than bone and are even harder than tooth enamel, the hardest substance in the human body (the more you know). The scales on the snails’ feet are also made of these same layers of material, and are just as hard as the shell. These scales are likely designed to repel the attacks from predatory snails, which shoot their prey with venom-laced harpoons.
Exactly how the snails build this armor is not entirely known, but we have some clues. Many bacteria can be found on the outside of these snails’ shells and scales. These microorganisms may help the snail to pull iron sulfides out of the water or may build a scaffolding onto which the iron compounds harvested by the snail can be added. Interestingly, the snails don’t actually need to construct these shells, and in places where the water doesn’t contain enough iron sulfide, they only form regular old calcium carbonate shells, changing their shells to a bright yellow and their scales to a tooth-like white.
Besides the positively medieval suits of armor they rock, scaly-foot snail behaviors and lifestyles are really weird. In order to understand just how weird they are, we need to talk about their habitat—hydrothermal vents. Hydrothermal vents are fucking awesome, and I love them so much that I am having to restrain myself from writing a verifiable Russian novel about how goddamn cool they are. Instead, I’ll write here what you need to know to understand the snail’s lifestyle and maybe I’ll rant about hydrothermal vents another day (you bet I will). So while we may think of the ocean as sunny and bright blue, most of it is actually quite dark. Below 200 meters (~650 feet) or so, very little light is able to penetrate through the water of the ocean, and below 1000 meters (~3300 feet), basically all sunlight is completely extinguished, plunging everything into eternal darkness. This is known as the Abyssal Zone, and in it live some of the absolute weirdest animals on Earth, scaly-foot snails among them.
Animals that live in the abyss have a lot of things to worry about (though unlike me they don’t have to worry about being ugly since no one can see them. The bastards have it too good). That deep in the ocean, the sheer weight of the water above puts an incredible amount of pressure on everything. The pressure of the abyss is so massive, in fact, that if you went there in a scuba suit, the pressure would collapse your chest cavity and crush your lungs like soda cans before forcefully filling them with seawater (you would not be crushed physically, though, which is what I thought would happen when I started reading about this). That seawater would be freezing cold, too, as most of the water within the abyss is near-freezing. Only animals specially-adapted to the cold can survive here, and many of them are so well-adapted that they cannot survive at all in warmer climates.
Finally, there is the matter of food. We don’t think about it often, but all of the energy that you consume in your food comes from the sun. Plants (or algae, or occasionally bacteria) fix sunlight into usable energy by photosynthesis, and that energy can then be utilized by other living things. You are able to breathe and walk and talk and look at memes because you acquired energy from your food that ultimately came from sunlight. In the abyss, however, there is no sunlight, and so plants cannot photosynthesize. As such, animals that live in the abyss have to get really creative when it comes to finding food. Many are scavengers, eating the dead stuff that sinks into the depths from the upper layers of the ocean. But some organisms reject the surface world completely and form ecosystems all on their own, ecosystems which are completely disconnected from the sun and its energy. These ecosystems come in two forms: methane seeps and hydrothermal vents.
In a nutshell, a hydrothermal vent is a spot where magma from beneath the Earth mixes with seawater. The seawater sinks down into a crack in the Earth’s crust, gets really fucking hot due to the magma, and bursts back up out of the crack, carrying with it some of the dissolved minerals and chemicals from the magma in the form of massive plumes that look like underwater smoke. Over time, minerals from these plumes build up in a chimney-like shape, creating structures known as black smokers. In addition to making these structures, hydrothermal vents fill the nearby water with a chemical soup rich in hydrogen sulfide and other organic nutrients. If most creatures tried to eat this chemical soup, they’d just get a mouthful of muddy garbage that tastes like rotten eggs (and would then suffer
an excruciating death from being, you know, in the abyss), but some deep-sea bacteria can turn the hydrogen sulfide in this soup
into usable nutrients through a process called chemosynthesis. The entire food chains of
hydrothermal vents are built around these chemosynthetic bacteria, as opposed to being
built around plants like food chains are in the surface world.
Okay, hydrothermal vent tangent over. Back to the snail. Scaly-foot snails have adapted to their hydrothermal environment in a few key ways. The snails live in dense clusters at the base of black smokers. In this zone, they are able to acquire nutrients from the smokers, but the water stays quite cold, only around 2 degrees celsius (35 degrees Fahrenheit). The snails survive quite well in this environment, as their bodies are adapted to function despite the cold. The weirdest thing about these snails, though, is that they never eat. While they do have mouths, they are quite weak, and the snails’ stomachs never have food in them.
Instead of eating, these snails have an enlarged esophagus which is filled to the brim with bacteria capable of performing chemosynthesis. The snails swallow that nutrient-rich organic soup I was ranting about earlier and the bacteria convert that soup into energy that the snail can use. In exchange, the bacteria live inside of the snail and are protected from the various other creatures on the vent that would love to chow down on them. The arrangement is kind of like if one day you got strep throat, but instead of taking antibiotics and drinking hot tea to make it go away, you trained your strep throat to make little tiny pieces of ground beef and drop them down your esophagus to feed you. This is a form of Mutualistic Symbiosis, a process by which two or more organisms work together to survive, each benefitting the other.
This kind of relationship between bacteria and animals isn’t unique to the snail—many hydrothermal vent critters, from the tube worm to the yeti crab, possess reservoirs of chemosynthetic bacteria in their bodies that produce food for them. Animals on the surface partner mutualistically with bacteria as well, including us humans. Unfortunately, our gut microbes only hang out in our large intestines to help us digest things and can’t synthesize chemicals in the air to make cheeseburgers for us. Damn layabouts.
Despite their badass armor and ability to synthesize nutrients from magma, these very cool snails face some major threats to their continued existence. Hydrothermal vents are fairly rare phenomena which can only exist at specific locations along the ocean floor, places along the edges of tectonic plates where the Earth’s crust is thin enough to crack and cause the seawater to mix with magma. Between hydrothermal vents are vast swaths of freezing-cold, empty ocean, underwater deserts where chemosynthetic bacteria have little to no nutrients to feed on. The distance between one hydrothermal vent and another can be up to 1000 kilometers, about the distance from New York to Cincinnati, Ohio. As such, most hydrothermal vent species live only on one or two vent fields in the entire world, as it is very unlikely for a population of them to survive migrating from one vent to another. Scaly-foot snails have only been identified in three of these vent ecosystems, and the total area of all of these ecosystems combined is only about 300 square kilometers, an area about the size of Fresno, California.
Remember when I said that hydrothermal vents contain minerals that filter up from magma deposits? Some of those minerals happen to be of commercial value to humans, such as gold, zinc, copper, and silver. By mining the seafloor, humans can harvest these metals, and this has not escaped the notice of mining companies around the world. The Longqi Vent Field, one of the three fields where Scaly-foot snails have been observed, has already been licensed to the Chinese Ocean Minerals Resources, Research and Development Association (COMMRDA, the world’s worst acronym), who have permission to explore the area to identify the presence of valuable minerals. Twelve minerals of potential use to humans have been identified at Longqui, and it is possible that in the future the COMRRDA could begin to extract these metals from the area, destroying the incredibly unique habitats where these animals live. Another of the other vent fields where Scaly-foot Snails have been found, the Kairei Vent Field, is under a similar exploratory license to the Federal Institute for Geosciences and Natural Resources of Germany (FIGNRG, somehow an even worse acronym than COMRRDA). FIGNRG, incidentally, is also the sound an extremely drunk guy makes while mumbling about how he lost trivia night at the Buffalo Wild Wings.
In 2019, the Scaly-foot Snail became the first species to be listed as Endangered by the International Union for the Conservation of Nature (IUCN) due to the threat of seabed mining. Now, three years later, over 100 deep-sea species have joined the snails on the IUCN Red List for the same reason. With the snails naturally occurring in so few locations, any disturbance to their ecosystems has the potential to decimate their populations. Hydrothermal vents are really difficult to study since they are so difficult to access. Human divers would die pretty much instantly if they attempted to swim down there, and remote-operated submersibles capable of operating at those depths are expensive. As such, we don’t really know what kinds of disturbances vent habitats can handle. In plenty of other locations around the world, we have seen that even small human activities can have devastating consequences on local wildlife. Additionally, seabed mining, even in small amounts, has the potential to disturb the system of underground vents that allow the seawater to mix with magma, cutting off the black smokers and eradicating the entire ecosystem.
The United Nations International Seabed Authority (ISA, a much nicer acronym) oversees the leasing of deep-sea ecosystems for exploration. Founded in 1994, the ISA oversees all “mineral-resources-related activities” on the seabed, with the goal of preserving the seafloor as “the common heritage of mankind.” In theory, this organization is meant to prevent individual nations from profiting off of the seafloor, keeping that area safe from disturbances. Despite this, the ISA has allowed exploration by government bodies with the goal of assessing the viability of resource extraction, something which puts these habitats in jeopardy.
Scaly-foot Snails stand as a living testament to the adaptability of life, but also its fragility. These strange creatures can survive pressures way higher and temperatures way lower than any surface-dwelling animal. They have developed armor in a way that no other animal on Earth has, and manage to feed themselves despite living in an ecosystem with zero access to the life-giving sunlight most animals require for life. But yet, our desire to extract resources to further our species may put the very existence of these snails, and many other deep-sea animals, at stake. If we as a species really do want to preserve the oceans as the common heritage of mankind, we need to recognize that our planet does not just belong to us, but to a multitude of creatures which deserve to continue existing just as much as we do.
Sources and More Information:
Australian Academy of Science: "She Sells Sea Shells: The Secret Life of One of the Ocean's Wonders"
Chen et al., 2015. "The ‘scaly-foot gastropod’: a new genus and species of hydrothermal vent-endemic gastropod (Neomphalina: Peltospiridae) from the Indian Ocean." Journal of Molluscan Studies.
PEW: "Behind the Quest to Protect the Unique Life Around Deep-Sea Vents."
Video Sources:
Mind Field: What Is the Scariest Thing? (Extremely good, Emmy-nominated episode of Michael Stevens' Mindfield about the biology and psychology of fear).