New genetic information on the brachiopod Lingula anatina shows that the biomineralisation of calcium phosphate has evolved multiple times. In case you were wondering a brachiopod is a bit like a mollusc except that their two shells are normally assymetric. Lingula anatina has a shell composed of calcium phosphate and proteins. Sound familiar? It should, that is the same basic components of bones! So are lingulid brachiopods our distant ancestors? No. The genes responsible for biomineralisation in Lingula are independent of the genes used by vertebrates.
The evolutionary origins of lingulid brachiopods and their calcium phosphate shells have been obscure. Here we decode the 425-Mb genome of Lingula anatina to gain insights into brachiopod evolution. Comprehensive phylogenomic analyses place Lingula close to molluscs, but distant from annelids. The Lingula gene number has increased to ~34,000 by extensive expansion of gene families. Although Lingula and vertebrates have superficially similar hard tissue components, our genomic, transcriptomic and proteomic analyses show that Lingula lacks genes involved in bone formation, indicating an independent origin of their phosphate biominerals. Several genes involved in Lingula shell formation are shared by molluscs. However, Lingula has independently undergone domain combinations to produce shell matrix collagens with EGF domains and carries lineage-specific shell matrix proteins. Gene family expansion, domain shuffling and co-option of genes appear to be the genomic background of Lingula’s unique biomineralization.