page_title: Scaly-foot snail
section_title: Shell
hierarchical_section_title: Scaly-foot snail / Description / Shell
caption_attribution_description: English: Left to right: -2450m, Kairei vent field (25°19.239S, 70°02.429E), Central Indian Ridge; -2785m, Longqi vent field (37°47.03'S, 49°38.97'E), Southwest Indian Ridge (Type locality); -2606m, Solitaire vent field (19°33.413S, 65°50.888E), Central Indian Ridge, Mauritius.
context_page_description: Chrysomallon squamiferum, commonly known as the scaly-foot gastropod, scaly-foot snail, or sea pangolin, is a species of deep-sea hydrothermal-vent snail, a marine gastropod mollusc in the family Peltospiridae. This vent-endemic gastropod is known only from deep-sea hydrothermal vents in the Indian Ocean, where it has been found at depths of about 2,400–2,900 m. Chrysomallon squamiferum differs greatly from other deep-sea gastropods, even the closely related neomphalines. In 2019, it was declared endangered on the IUCN Red List, the first species to be listed as such due to risks from deep-sea mining of its vent habitat that also produce high-quality metal ores.
  The shell is of a unique construction, with three layers; the outer layer consists of iron sulfides, the middle layer is equivalent to the organic periostracum found in other gastropods, and the innermost layer is made of aragonite. The foot is also unusual, being armored at the sides with iron-mineralised sclerites.
  The snail's oesophageal gland houses symbiotic gammaproteobacteria from which the snail appears to obtain its nourishment.
context_section_description: The shell of these species has three whorls. The shape of the shell is globose and the spire is compressed. The shell sculpture consists of ribs and fine growth lines. The shape of the aperture is elliptical. The apex of the shell is fragile and it is corroded in adults.
  This is a very large peltospirid compared to the majority of other species, which are usually below 15 millimetres (³⁄₅ in) in shell length. The width of the shell is 9.80–40.02 mm (0.39–1.58 in); the maximum width of the shell reaches 45.5 millimetres (1.79 in). The average width of the shell of adult snails is 32 mm. The average shell width in the Solitaire population was slightly less than that in the Kairei population. The height of the shell is 7.65–30.87 mm (0.30–1.22 in). The width of the aperture is 7.26–32.52 mm (0.29–1.28 in). The height of the aperture is 6.38–27.29 mm (0.25–1.07 in).
  The snail's shell is also unusual. The shell structure consists of three layers. The outer layer is about 30 μm thick, black, and is made of iron sulfides, containing greigite Fe₃S₄. This feature makes this gastropod the only extant animal known so far that employs this material in its skeleton. The middle layer (about 150 μm) is equivalent to the organic periostracum which is also found in other gastropods. The periostracum is thick and brown. The innermost layer is made of aragonite (about 250 μm thick), a form of calcium carbonate that is commonly found both in the shells of molluscs and in various corals. The color of the aragonite layer is milky white.
  Each shell layer appears to contribute to the effectiveness of the snail's defence in different ways. The middle organic layer appears to absorb mechanical strain and energy generated by a squeezing attack (for example by the claws of a crab), making the shell much tougher. The organic layer also acts to dissipate heat. Features of this composite material are in focus of researchers for possible use in civilian and military protective applications.
caption: Individuals from the three known populations of C. squamiferum: 
  Kairei, Longqi, Solitaire (left to right)
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