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The Volcano-Dwelling Snail (Chrysomallon squamiferum)

Updated: Feb 28, 2021

This snail is more commonly known as the scaly-foot snail or iron snail. It is a species of gastropod with an iron shell and iron scales. This is a snail with the heart of a dragon. Let's discover more about these deep-sea marvels.

Scaly-foot snails are a genus and species of deep-sea gastropod that all appear to have the ability to sequester iron metal ions forming an iron sulfide coating on their shells, along the sides of their bodies, and on parts of their foot. The Kairei population (represented in the image above) is the population of this species that is most well known for its dark shell and scales. Kairei represents a hydrothermal region along the Indian Central Ridge in the Indian Ocean that is rich in iron compounds. It is postulated that bacteria on the snails may be producing sulfur-rich compounds that attract iron ions from the water forming iron-sulfide.

A lighter shelled population due to no iron mineral deposits.
Same species but at a neighboring vent with much less iron ions coming from the vent. Image Source: Wikipedia CC BY 2.5


Scaly-foot snails of the Kairei population only exist along the Indian Central Ridge. This area is where the continents of Africa and Indo-Australia meet underwater. The joining of these plates form uplifts in which small fissures appear. As water seeps down into the cracks, it reaches volcanic molten rock. This produces steam and forces the hot gases upward eventually venting out forming hydrothermal vents. Communities of organisms form around this heat source where temperatures can reach over 700°F just inside the vent and ~400°F in the areas immediately surrounding the vent. Temperatures cool quickly however the further you are from the opening. Despite their nickname, these snails do not reside in volcanos but rather live near the hydrothermal vents produced by them. As they are not very close to the opening, they can enjoy mild temperatures of ~68°F or so. The scalding water ripples as seen in the image below, are the result of temperature variations in the water, much like how a mirage works.

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Like some magical, immortal dragon, this snail doesn't need to eat other organisms. It instead relies on bacteria that reside in a special organ that provides it with the energy it needs. This symbiotic relationship is believed to have been in place for hundreds of millions of years. The bacteria depend on the snails to provide oxygen and access to the sulfur-rich compounds, they in-turn provide organic compounds for energy and perhaps materials it needs to build its iron coating for its shell.


Scaly-foot snails are simultaneous hermaphrodites which means they can generate eggs and sperm simultaneously and don't switch between gamete formation and accessibility. This ability to self-fertilize reduces its genetic diversity. This lack of genetic diversity between thermal vent regions provides some evidence that the snail larvae must engage in a planktonic stage and simply drift to nearby vents.

Weird fact: Compared to its other snail cousins, this species has evolved to have its gonads outside of its shell rather than inside.


Chrysomallon reside around mineral-rich vents; as a result, mining threatens their existence. They are now considered an endangered species according to the IUCN. This status however has not afforded their habitat any protection from mining.

Featured Video

Learn more about this amazing organism via the video below. Thanks for reading!

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