Aragonite shells are more ancient than calcite ones in bivalves: new evidence based on omics

Two calcium carbonate crystal polymorphs, aragonite and calcite, are the main inorganic components of mollusk shells. Some fossil evidences suggest that ara- gonite shell is more ancient than calcite shell for the Biv- alvia. But, the molecular biology evidence for the above deduction is absent. In this study, we searched for homo- logs of bivalve aragonite-related and calcite-related shell proteins in the oyster genome, and found that no homologs of calcite-related shell protein but some homologs of ara- gonite-related shell proteins in the oyster genome. We explained the results as the new evidence to support that aragonite shells are more ancient than calcite shells in bivalves combined the published biogeological and sea- water chemistry data.