Deuterostome phylogeny and the origin of pharyngeal segmentation. Acquisition of characteristics is indicated in blue, loss in red. The proposed stem deuterostome is likely to have possessed pharyngeal slits. These have been secondarily lost in echinoderms but retained in the hemichordates. Within the chordate lineage, cephalochordates (for example, amphioxus) and urochordates retain pharyngeal slits in the adult form (indicated by blue lines). Within the vertebrate lineage, there was a shift away from filter feeding towards active predation. Modification to the pharyngeal segments included a reduction in number, a neural-crest-derived endoskeletal support, and arch arteries providing vasculature for the gills.