Coatings on shells from hydrothermal vents

Shells of marine gastropods from hydrothermal vent environments are coated with inorganic materials of unknown composition. Conversely, their fossil equivalents are known exclusively from outer moulds in pyrite (FeS₂), with no shell material left. An international team of researchers from the Institute of Paleobiology, Japan, Germany, and United Kingdom studied coatings on gastropod shells from four active hydrothermal vent sites. The study revealed that the coatings on gastropod shells are composed of compounds with chemistry close to that of the emitted fluids. The pyrite was the only mineral identified, with the remainder comprising most likely amorphous substances.

Figure: Shell of gastropod Desbruyeresia marisindica from Kairei hydrothermal vents in the Indian Ocean, covered with inorganic coatings (A), with cross section through this shell showing morphology of inorganic coatings (B) and close-up on a fragment showing structure and shell/coating spatial relations (C). Distribution of some elements (oxygen, manganese, calcium, iron, copper, and phosphorus) in a fragment of coating illustrated in (C) is shown in lower two rows.