The origin of barnacles (Thecostraca, Cirripedia)

Abstract

I claim that hybridogenesis has played a vital part in the evolution of the Thoracica, Acrothoracica, Rhizocephala and Facetotecta. Hybridogenesis is the generation of new life forms and new life histories by sexual hybridization. It includes larval transfer, which explains the origins of all larvae, and component transfer, which explains the origins of cnidarians, lophophorates and thoracicans. I propose that adult thoracicans are descended from a hybrid between a crustacean and a non-arthropod, the genomes of which are expressed together. They are concurrent chimeras. Adult acrothoracicans are equivalent to the crustacean part of thoracicans. Nauplius larvae were added to the life histories of thoracicans and some acrothoracicans by later hybridizations. Adult rhizocephalans and juvenile facetotectans have no arthropod characteristics, and I claim that both these taxa acquired nauplius and cypris larvae by hybrid transfer. Extreme differences between the mitochondrial genomes of a sacculinid rhizocephalan and thoracicans are consistent with this view of rhizocephalan evolution. The Rhizocephala and Facetotecta are not members of the Cirripedia or the Arthropoda.