Abstract:  Pharyngeal gill slits are a key synapomorphy for defining the Deuterostomia. The Cambrian vetulicolians have been demonstrated to be the most ideal stem-group deuterostomes, based on their possession of a series of gill slits combined with primitive characters. The vetulicolian gill slits are justified to be homologous to pharyngeal gill slits of deuterostomes, with their primitive function as ventilation openings to expel seawater from the pharyngeal cavity. The emergence of the phylum Vetulicolia during the Cambrian explosion of life signals the birth of the pharyngeal gill slits in deuterostomes, which triggered a revolution in efficiency of basal metabolism (not least feeding and respiration) in the kingdom Animalia and paved the way for the subsequent rise
of the Deuterostomia.

Key words: Cambrian, Chengjiang biota, Vetulicolia, Deuterostomia, pharyngeal gill slit