Phylogenomics of crabs provides insights into their origin and evolution

Crabs encompass the infra-orders Brachyura and Anomura, collectively constitute the clade Meiura within order Decapoda. Despite their considerable diversity, genomic resources for crabs remain scarce, hindering our understanding of their phylogeny and genetic mechanisms underlying such unique traits as carcinization. To address these questions, here we sequenced genomes of 10 crab species covering all currently controversial taxonomies at section level. Our whole-genome phylogenetic results support Raninoida is closer to Eubrachyura rather than Dromiacea, challenging the traditional classifications. Notably, the freshwater crab subsection Potamoida, represented by S. planum, is found to be more closely related to subsection Thoracotremata than to Heterotremata as previously suggested, indicating that crab classification based solely on morphology may be misleading. Our results also clarify that the family Gecarcinidae should be classified into Thoracotremata, contrary to previous placements in Heterotremata. Comparative genomic analyses identified lineage-specific families related to crab traits, including ionotropic glutamate receptors, neurotransmitters, and energy metabolism. Additionally, transcriptomic studies of Chinese mitten crab larval stages suggest that some lineage-specific genes such as ghrA, and TCB2, may account for the prominent carcinization in brachyurans. This study not only significantly expands the genomic repository for crabs, but also provides insights into the phylogeny and trait evolution of crabs.