Tough shell to crack: The deep-sea snail made of iron

It seems impossible that any living organism can thrive, let alone survive, thousands of feet below the Indian Ocean where deep-sea hot springs spew columns of boiling water. Yet the Scaly-foot Gastropod (Chrysomallon squamiferum) goes on to prove that even in the harshest of conditions, the living goes on adapting, evolving and even growing a suit of armour to suit its toxic utopia.

Iron tough

The scaly-foot gastropod is a species of deep-sea hydrothermal-vent snail living up to 2,800 metres below the ocean’s surface. They were first discovered at the turn of the millennium at the Kairei hydrothermal vent field located on the Central Indian Ridge. The incredible thing is that they were living on the bases on black smokers, which is a place on the bottom of the seabed where tectonic plates collide and move apart from each other, allowing magma to heat and water to boil, rising in magnificent chimney-like structures.

Here’s the kicker though. The water in these vents are high in sulphides and metals, which the snails have integrated into their shell. The entire creature is covered in an iron compound of pyrite and greigite. The middle layer of this snail’s shell is a thin protein coating similar to the common snail, while the inner layer is constructed of aragonite, which is a type of calcium carbonate also commonly found in coral. It has a soft, fleshy foot that on the surface looks similar to the snails found in our gardens but is protected by hard mineralised scales made of iron sulphides.

Iron snail

Image: Stefan Bengtson

It is the only living creature on earth to utilise iron in this way. And because it’s partly made from greigite, it’s magnetic too!

Its iron casing isn’t the only impressive characteristic of the scaly-foot snail. The shell also possesses its very own superpowers and when hit by crabs (a common enemy), its designed to micro-crack, but in a way that absorbs energy, preventing larger cracks from forming. It’s middle layer then acts as further padding to the energy of the blow, protecting the brittle third layer.

Studying organisms who have self-optimised for intense environments through millions of years of evolution could be key to protecting human life too. Scientists believe that the three-layer design of the scaly-foot could be used to improve human body armour or helmets without increasing weight for the wearer.

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Featured image: David Shale