Please see the image. This differs from Fig. 33.5: the body cavity should not, like any other one trait, be the exclusive data for building a phylogeny due to the possibility of parallel evolution of one trait causing confusion. ______
Work Step by Step
The particular kind of body cavity could evolve more than one, which is especially clear given what we know now about the genetics of development. So, any one trait could give a highly misleading phylogeny, and multiple traits need to be used to arrive at the evolutionary scenario which actually occurred.