If you heard about an animal that could withstand the heat of a volcano and clad itself in iron, you might imagine a dragon. But the amazing animals that have these superpowers are in fact… snails!

Type specimens are kept in the National History Museum of London.

Also known as scaly-footed gastropods or sea pangolins, these molluscs live endemically around deep-sea hydrothermal vents in the Indian Ocean.

For the first time, the genome of these hardy animals has been decoded by a team at the Hong Kong University of Science and Technology. The motivation for this research was to better understand how early life in the deep sea may have evolved and survived. It is currently theorised that life may have originated around hydrothermal vents due to the chemical abundance in those areas. Applications in other fields such as medicine are also a possibility.

The only known animals to incorporate iron into their (exo)skeletons, the snails possess a gene named MTP9 (metal tolerance protein 9). The research team found that, when comparing a population with an iron-rich environment to that of an iron-poor one, the iron-rich population had a 27-fold increase in MTP9.

It is thought that the protein specifically allows tolerance for the environmental iron ions that interact with the sulphur in their scales, which creates iron sulphides. Iron sulphides – specifically greigite, Fe₃S₄ – make up the outer layer of the armour, while the middle is of an organic compound made by other gastropods (periostracum) and the innermost layer is composed of aragonite. Aragonite is found naturally in almost all other mollusc shells as well as corals. It is recommended as substrate in marine aquaria to mimic that of coral reef habitats.

Individuals from the three known populations of C. squamiferum: Kairei, Longqi, Solitaire (left to right).

By Chong Chen – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=39716931

Distribution of C. squamiferum in the Indian Ocean.
By User:Snek01 – Own work Created by Michal Maňas in QGIS.

These snails have other peculiar features alongside their incredible adaptations.

• The foot (bottom of the body) is also armoured with iron-mineralised structures known as sclerites. These almost appear like layers of chainmail. This scaly appearance may be why they are sometimes referred to as sea pangolins too.
• Pyrite (fool’s gold) is also incorporated into the sclerites.
• Their hearts are 4% of their body volume.
• They have no eyes and cannot withdraw fully into their shells.
• They obtain all their nutrition from symbiotic gammeproteobacteria that live in their oesophageal gland.

Why wear the armour? Likely a happy by-product of withstanding the iron-rich environment of deep-sea vents, it certainly does a good job of protecting them. The layers are thought to work in conjunction to absorb mechanical stress, and the middle, organic layer can dissipate heat. This prompts research into heat-resisting composite materials that may be of use in sectors such as the military. Despite the extremes of the hydrothermal vent reaching as high as 464°C, the snails favour a cosy water column that is between 2°C and 10°C.

In 2019, these snails became the first species to be listed as Endangered by the IUCN due to deep-sea mining – its iron-rich habitats also produce desirable, high-quality ores. For its sake as well as other deep-sea organisms, regulation of deep-sea resource acquisition needs to be regulated so as not to cause extensive environmental and ecosystem damage.