It is indeed challenging to fathom there are life forms hundreds of feet beneath the surface of the Indian Ocean, wherein geothermal eruptions essentially boil the seawater. But, as we see it, life has a way of seeping in even in some of the most hostile environments. One example is the chrysomallon squamiferum, a snail-like organism with some of the most incredible body armor in the natural world. The strange iron-shelled snail dwelling in volcanic vents can withstand extreme heat and pressure while collecting metal fragments from the environment to strengthen its spiky coat.

It is also referred to as the sea pangolin, the scaly-foot gastropod, or the scaly-foot snail. This wiggly mini brave man, whatsoever you term it, lurks in the darkest and innermost sections of some of the world’s hottest underseas, protected by an iron sulfide shell that allows it to survive in severe heat.

Researchers have discovered the secret of the volcano-dwelling snail and its metal shell after experts deciphered its DNA for perhaps the first time in history. This scaly-foot snail thrives in the problematic living circumstances of undersea thermal vents. Experts predict that exploring the composition of this creature may disclose the intricacies of how early life originated and uncover its tremendous potential for medical and other uses.

Description

Volcano snails
Volcano snails | Image Credit – Smithsonian Magazine

Chrysomallon squamiferum is a huge Peltospiridae gastropod, no doubt! Adult snail shells are typically 32 mm in diameter, but they can extend to be as large as 45.5 mm. These shells are spherical and curled in three swirls. Like the first swirl, the spire is depressed, and the swirls are tightly coiled. The shell does not have prominent lamellar sculpture-like regular snails, but it contains delicate development patterns and faint, closely-formed ribs. A black coating of iron sulfide frequently coats the shell’s surface.

Snail feet are enormous and wrapped in hundreds of overlapped tough dermal sclerites, giving the snail its trademark. The foot’s length and armor prohibit it from being entirely retracted inside the shell’s opening. The armored sclerites adorning the scaly-foot snail’s foot are thought to protect the specimen from predators. It is also hypothesized that symbiotic bacteria residing on the snail’s foot in between overlapped sclerites aid in producing iron sulfide layers on the sclerites.

Habitat

Hydrothermal vent regions
Hydrothermal vent regions | Image Credit – Flickr

Scaly-foot snails are deep-sea gastropods that live in hydrothermal vent regions at depths of 2,400 to 2,900 meters. The Longqi area on the South West Indian ridges and the Kairei and Solitaire fields on the Central Indian ridges are the only confirmed occurrences in the Indo-Pacific. Investigators can spot the Scaly-foot snail at the bottom of black-smoker chimneys and in scattered fluxes, where it lives a sedentary life. It is projected that its total distribution region is 0.27 km square.

Feeding Habits

Volcano snails feeds on bacteria
Volcano snails feeds on bacteria | Image Credit – Pixabay

Several astonishing creatures have evolved to exist in these hazardous utopias across historical timeframes, flourishing by utilizing the energy provided by bacteria and other minute living organisms. Similarly, volcano snails rely on bacteria that live in a specific organ that gives them the energy it requires. 

This mutually beneficial interaction is thought to have existed for millions of years. The bacteria rely on the snails for oxygen and the availability of sulfur-rich chemicals. The snails, in exchange, receive organic molecules for energy and maybe ingredients for the snail’s iron covering. To put it another way, this one-of-a-kind snail has a food factory within its body and does not require feeding! Doesn’t that sound like a dream? This is most definitely why it can reach a size of 45mm, even though most of its close cousins without endosymbionts are just 15mm or less.

Reproduction

The Scaly-foot snail is a concurrent hermaphrodite with no sex determination. The snail has no copulatory organs, but it does contain gonads and a spermatophore packaged structure in the head-foot area. The vaginal aperture of the scaly-foot snail is very basic. 

They may produce eggs and sperm simultaneously but do not alternate between gamete creation and availability. Because of its capacity to self-fertilize, it has less genetic variety. This loss of genetic variation across thermal vent sites suggests that snail larvae must go through a planktonic phase before drifting to neighboring outlets.

On the brink of extinction

As fascinating as these critters are, they are on the verge of disappearing owing to deep-sea mineral mining, which could have a bearing on the Earth’s shifting climate. The International Union for Conservation of Nature (IUCN) listed the volcano snail as an endangered species in 2019. In recent times, the population has decreased significantly. While they can be found in abundance in the Longqi vent field, their numbers are rapidly dwindling in other parts of the globe.

Deep-sea mining is the most severe problem for the snail’s survival. Polymetallic sulfide mineral deposits are coveted for their high concentrations of rare metals, such as copper, silver, and gold, which occur in profusion around hydrothermal vent sites. As a result, the gastropods’ survival is constantly threatened by mining activities that disrupt their ecosystem. Although there are no active conservation and restoration attempts to rescue the volcano snail, their mere existence warrants additional sustainability studies. 

Further investigation is recommended to evaluate whether the populations are vulnerable to mining perturbation, verify whether the organisms are prevalent at any other vent site along the Central and South Indian grooves, and understand the species’ low propagation and the reproductive process. These studies will aid in the reassessment of the species’ vulnerability and conservation status.

And, the best part at last – Three folds of protection!

Three folds of protection
Three folds of protection | Image Credit – Australian Geographic

The casing and foot-scales of the volcanic gastropod have three unique coatings that shield the snail against enemies and the hostile climate in which it dwells. Its exterior is essentially the same as other mollusks and snails, with an additional layer of plate fastened on top. There are two separate structural divisions in a regular garden snail shell; in the scaly-foot gastropod, there are three.

The inner part of their shell comprises aragonite, a calcium carbonate that can be present in the shells of mollusks and corals. This inner layer aids in heat dissipation, preventing the snail from succumbing to a gradual, volcanically produced stew. The middle layer, similar to the outermost biological surface present in other gastropods, is the thickest of the three, measuring roughly 150 mm. This stratum appears to operate as cushioning, absorbing the mechanical stress and energy created by a crushing assault, rendering the shell considerably more brutal and more challenging to break.

The outermost part, though, is the most remarkable. It is composed of iron sulfides, including pyrite and greigite, and is very thick. This mollusk is the only metazoan and the only creature known to use such a component in its exoskeleton. The outer shell’s greigite nanoparticles primarily act as a shock absorber. 

When a snail’s shell is put under extreme pressure, it fractures around the granules, absorbing energy, neutralizing and damaging the predator’s claws. Countless microcracks scatter the shell, absorbing the stress while preventing massive fractures from appearing on the shell, which would have been deadly to the snail. Isn’t that some of the best defenses? 

Facts

  • Scientists initially identified Scaly-foot snails in the Indian Ocean’s Kairei outlet area in 2001. Its finding came as a complete shock, as it was highly unusual even among species adapted to survive in such boiling openings.
  • It is the only life form documented to integrate iron into its skeleton while withstanding extreme temperatures, tremendous pressure, intense acidity, and low oxygen levels.
  • Marine biologists are particularly interested in the scaly-foot snail because of its capacity to tolerate high pressures, temperatures, and acidity.
  • To begin with, this is a tiny creature with a large heart – about 4% of its whole body volume, to be accurate. This gives it an enormous heart in the animal kingdom in terms of body size, allowing the snail to survive in an oxygen-depleted atmosphere.
  • It is the only snail alive with armor-like plates, formerly a widespread feature of gastropods during the Cambrian era, approximately 540 million years ago.
  • Unlike its other snail relatives, this species’ gonads have evolved to be outside of the casing than inside.
  • Iron compounds, primarily pyrite and greigite, blanket the animal’s body. The animal attaches to magnets because greigite is magnetic. The scales are thought to serve as either defense or detoxification, but their true purpose is unknown.
  • The snail’s casing is so unique that the US military is supporting the investigation into it in the quest to develop new military armor models based on it.
  • Although it was discovered in 2001, it was classified and detailed in a research paper only in 2015.

To Conclude

There are apparently no conservation and mitigation measures at any outlet sites where the snails have been discovered. Furthermore, two of the snails’ three homes have already been formally approved for mining activities to proceed, and it’s unclear whether the snails will be able to migrate to new regions. Volcano snails are on the verge of extinction. And this is yet another proof of how humanity has failed, once again!

Shradha Bhatta holds a Bachelors’s Degree in Social Work along with a Post-graduate degree in Project Management from Georgian College in Canada. Shradha enjoys writing on a variety of topics and takes pleasure in discovering new ideas. She likes traveling and spending time with nature. She is a very people-person who loves talking about climate change and alerting people to go green!