Crown group deuterostome relationships. (a) Diagram showing the relationships between crown group (green), stem group (red) and total group (yellow). A1 and A2 are sister taxa within the crown group; † = extinct taxon. Note that members of the stem group must have at least one but not all of the synapomorphies defining the crown group to be recognized as such. (b) Deuterostome relationships as deduced from molecular data  with vetulicolian placement following Ou et al. . (c) Deuterostome relationships that would be inferred (wrongly) from adult morphology alone. The position of vetulicolians assumes their pore structures are indeed pharyngeal gill slits.