Episode 135 – Scaly Foot Snail: Snail Mail Armor

In this animal podcast episode, we talk about the scaly foot snail, an animal with metal armor.

“Today we’re talking about a metal mollusk, perhaps the most metal animal we’ve discussed.”

Iron is the ultimate symbol of impenetrability. In fact, an old naval vessel called the USS Constitution was nicknamed Old Ironsides in an Oliver Wendall Holmes poem because cannon balls were said to bounce off the ship’s sides. But is iron an defense mechanism unique to humans. For a long time we thought it was, but there’s a deep-sea extremophile that makes a home out of volcanoes and wears a suit of armor to bed. For the scaly foot snail, living the metal lifestyle is just one way to thrive against all odds in Life, Death, and Taxonomy.

Where Does the Scaly Foot Snail Live?

Lives only in the deep-sea vents of the Indian Ocean 1.73 miles below the surface (relatively close to Madagascar). Just like the giant tube worm, these guys love to hang out near underwater volcanoes. These black smokers are spewing piping hot chemicals and metals into the water at the bottom of the ocean where no light can reach.

Description of the Scaly Foot Snail

If you have trypophobia (fear of clusters of holes) or some analog of it, the scaly-foot snail may be pretty disgusting to you.

It’s got a pretty interesting shell. There are three whorls in the shell. In fact, it’s almost the perfect Fibonacci sequence – a mathematical golden spiral.

It also has an outer layer of an iron sulfide called greigite. And no other animal has a skeleton with greigite (the shell is technically the skeleton).

The middle layer is organic and may serve for heat and pressure protection (both for the crushing water and for crabs).

The inner layer is made of aragonite, which is common in mollusks. Perhaps the craziest thing about this guy is the scales on its foot.

As you know, a snail’s foot is pretty much the entire part of the snail you can see except for the eyes and antennae.

This snail’s foot is covered in hundreds of overlapping sharp-ish scales made of that same greigite called sclerites.

Our friend the chiton has sclerites covering its body, but these two species aren’t related. Ostensibly, this helps protect the snail from the heat of the vents it lives near.

The scaly-foot snail has no eyes or tentacles and can’t withdraw entirely into its shell.

Measure Up

Welcome to the beloved Measure Up segment. The official listener’s favorite part of the show! The part of the show when we present the animal’s size and dimension in relatable terms through a quiz that’s fun for the whole family. It’s also the part of the show that’s introduced by you when you send in audio of yourself saying, singing, or chittering the words measure up into ldtaxonomy at gmail dot com. We do have a new measure up intro today sent in by Andrew. He also said “What I think about every time a measure up segment comes on.”

Max Shell Width

  • 45.5 millimetres (1.79 in) the average is about 32 mm
  • How many large scaly foot snail shells go into the amount of rainfall produced by the Super Cyclonic Storm Gonu in 2007.
  • Hint: The Super Cyclonic Storm Gonu was the strongest cyclone that the Arabian Sea had ever seen. This area of the ocean usually doesn’t get large storms because of dry air coming from the Arabian Peninsula. 
  • 13.4 shells. The storm dumped 610 mm (24 inches) of rain and reached wind speeds up to 270 km/h (165 mph).

Living Depth

  • 2,780 metres (1.73 mi) in depth
  • How many ant hills made by the wood ant species Formica aquilonia go into the living depth of a scaly foot snail.
  • Hint: Wood ants are known to build complex nests in the coniferous forests of Asia and Europe.
  • 1,141.8 hills. The wood ant can build nests that reach eight feet high.

Scaly Foot Snail Fast Facts

What is the snail’s diet? The snail is actually a chemotroph, meaning it uses chemoautotrophy for nutrition.

This is an insanely complicated biochemical process. But it basically means the snail gets its energy from a symbiotic relationship with bacteria that can create energy from things like iron. Since there’s a lot of iron to be had at the mouth of an underwater volcano, there’s lots of “food” for the bacteria and the snail.

Scaly Foot Snail Major Fact: Old Iron Sides

The scaly foot snail is the only known animal that incorporates iron into its bodily defenses.

The snail has an iron reinforced shell and it has iron scale mail surrounding it’s foot. On a mollusk the foot is the part of the body that comes out of the shell to help them get around. This scale armor is made of sclerites, which refer to hardened body parts that aren’t related to bone or teeth. 

These sclerites are made of iron sulfides like greigite and pyrite, also known as fool’s gold. These metals surround epithelial tissue, which is the kind of tissue around your organs and in the top layer of your skin. This hardened armor most likely provides more protection than a typical chitin shell. Iron is more durable and less brittle than chitin and other organic material.

But how could it do that and why doesn’t everyone do that?

How the Scaly Foot Snail Handles Heavy Metals

First of all, too much heavy metals in an organic body can be toxic. In humans, a high iron level in your blood is called hemochromatosis. As a result, it can cause liver disease and heart problems. 

However, researchers have found snails around three thermonuclear vents in the Indian Ocean, two of which spew out high levels of iron. Only around these two vents do the snails have iron sulfide in their scales and shell.

We still aren’t sure how they incorporate the minerals into their armor. But brand new studies have unraveled some clues that were buried deep in the snail’s genome. To support this, a scientists in Hong Kong published a study in April of 2020 and they said, 

“We suggest that the ability of lophotrochozoan lineages to generate a wide range of hard parts, exemplified by the remarkable morphological disparity in Mollusca, draws on a capacity for dynamic modification of the expression and positioning of toolkit elements across the genome.”

What Does That Mean?

In terms that my brain can handle: the animals in this specific clade have a variety of anatomical armored oddities, especially mollusks. Because of this, scaly foot snails may be genetically suited to developing unique modifications to their armor. 

Scientists also discovered a gene called MTP9 or metal tolerance protein nine. It allows them to live in iron rich environments and even incorporate it into their bodies.

Ending: So put on a hearty shell, snuggle up to a warm vent, and always be sure that your endosymbionts oxidize ferrous irons into ferric irons in order to conserve electrons and reduce your respiratory chain through reverse electron transport like the Scaly-Foot Snail here in LDT.


Thank you to Casy for creating our theme song. To hear more of Casy’s music search Casy Michelle on Youtube

Thank you to Brian for creating the episode art. See more of Brian’s art at xNamaru on Instagram or Twitter.

Thank you to Doug for the animal suggestion for this episode!