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Deep below the Indian Ocean, in some of the most extreme environments on Earth, there's a snail that has developed a unique and incredible strategy for protecting itself from danger.  It builds itself an iron suit of armor.  It's called the scaly-foot snail, or Chrysomallon squamiferum, if you want to get technical.  Its name comes from the hundreds of stiff dark scales that cover its fleshy foot, the part of the snail's body it uses to scootch around.

These snails were first reported in 2001 living near hydrothermal vents on the seafloor.  They hang out in the geothermally heated waters while bacteria in their throats provide nutrients for them, and scientists were immediately intrigued by the snails' bizarre armored appearance.  Then, under closer inspection, things got even weirder.

It turns out those dark scales and the snail's shells are coated in a layer of iron.  Specifically, they contain iron sulfide compounds, which are molecular combinations of iron and sulfur.  In this case, the compounds are mainly pyrite, a mineral commonly called fool's gold, and (?~1:13), a mineral similar to magnetite, which makes the scales in shells slightly magnetic.

Interestingly, the snails only wear this suit of armor some of the time.  As of 2018, this species has been spotted at three different hydrothermal vent locations in the Indian Ocean, and at one of those locations, the waters lack iron sulfide, which is likely why the snails do, too, but in the other two spots, where the venting fluids are rich in iron compounds, the snails are somehow able to harness the minerals for themselves.  No other animal is known to incorporate iron into its skeleton or, in this case, exoskeleton, so scientists have been trying to figure out how these snails acquire their suits of armor and what they're used for.  

At first, researchers suspected the iron might come from bacteria that thrive in hydrothermal waters.  Specifically, bacteria that can survive the lack of oxygen because they essentially breathe sulfate instead, a process which produces iron sulfides as a side effect, but a 2006 study found that the chemical signature of the snail's iron is a better match for the iron-rich hydrothermal fluids than anything forged by bacteria.

So the snails seem to be building their own armor using iron from the water around them.  See, the iron in the water near these vents can naturally react with certain kinds of sulfur to make iron sulfides, so the idea, by regulating where and how the sulfur is available, the snails might have control over the formation of their mineral armor.  Exactly how they do this, though, isn't clear.

As for why they have this armor, well, protection from predators seems to be an obvious answer.  A 2010 study found that the iron shell has a multi-layered structure that makes it extra resistant to fracturing or bending.  On top of that, the foot scales are reportedly harder and stiffer than the enamel coating on your teeth, so the snail armor seems pretty perfect for resisting any attacks from the predatory crabs and snails in its ecosystem.  It may even serve as a model for humans to build extra strong materials, but we'll need to be careful not to wipe out the snails first.

See, in 2018, they were officially classified as an endangered species because the vents they live on are targeted for mineral mining.  Some of their habitat has likely already been disturbed, but hopefully, we can keep them around and they'll have a lot more to teach us.  

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