Meet The Sea Pangolin: A Vanishingly Rare Thermal-Vent Snail With Iron Scales

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A golden snail with a foot clad in iron scales seems like a creature from science fiction. But in a few remote spots of the Indian Ocean these snails are very real. “It looks like an armoured knight crawling around on the deep-sea floor,” says Julia Sigwart, a biologist at Frankfurt’s Senckenberg Research Institute and one of the only people to have seen a living scaly-foot snail (Chrysomallon squamiferum), also known as a sea pangolin.

The snails’ habitat is extreme. They live several miles below the ocean surface on searing hydrothermal vents, which are bathed in toxic chemicals and can reach temperatures of more than 300C (572F). The snails’ entire bodies and lifestyles revolve around bacteria growing inside a special pouch in their throat, which convert chemicals pouring out of the vents into energy and thereby provide all the snails’ food.

To keep their microbes well fed, scaly-foot snails evolved enormous gills to absorb oxygen and chemicals from seawater, then deliver it by way of their bloodstream and a hugely capacious heart. A human heart of equivalent proportions would be the size of our heads. In 2019, scientists worked out that the scales on the snails’ foot are not to protect against predatory attack but to avert a toxic threat that comes from within. The bacteria stashed in a scaly-foot snail’s throat release sulphur as a waste product, which is deadly to snails (it’s a common active ingredient in slug and snail-killing pellets).

The internal structure of their scales acts as tiny exhaust pipes, drawing the dangerous sulphur away from the snails’ soft tissues and depositing it as a harmless iron-based compound on the outside.

EDIT

https://www.theguardian.com/environment/2022/aug/03/discovered-in-the-deep-the-snail-with-iron-armour

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1. So the scales are made of iron sulfide, not metallic iron ...

The soft tissue core of each sclerite was covered in conchiolin, which was in turn covered with pyrite (FeS2) and greigite (Fe3S4), two forms of iron sulphide (Warén et al., 2003). Its shell was also covered in the same material, making it the only known metazoan to use iron in its skeleton (Yao et al., 2010).

https://academic.oup.com/mollus/article/81/3/322/1087877?

Journos, even in science mags, so often confuse "iron-containing" with "made of iron". Iron sulfides are hard minerals, but not metallic like iron (although greigite is ferrimagnetic, which is interesting).

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2. True - "ferrous scales", maybe?

But I have to admit, it does look unusually bad-ass for a snail, in a submerged Game Of Thrones kind of way.