Figure 1
From: Conservation and co-option in developmental programmes: the importance of homology relationships
Phylogeny of the Metazoa (adopted and simplified from [112-114]) depicting several new and controversial hypotheses of character evolution with regard to bilateral symmetry, central nervous system, segmentation, and steroid receptors. PDA: last common protostome-deuterostome ancestor; CNS: central nervous system. Filled bars indicate the origin of a character while open bars in the same colour indicate loss of that character. Open grey bars show that data for the assumed loss of steroid receptors are missing.