Figure 1

Bilaterian phylogeny highlighting the key features associated with body segmentation. For each segmented phylum (red) we listed a representative model organism, the germ layers that are primarily segmented (blue), the germ band development adopted among arthropods (purple), the segmentation dynamics (either sequential or simultaneous addition of segments, green), the initial patterning periodicity (orange), the tissue patterning that underlies segment formation (pink), and whether posterior growth occurs during segmentation (yellow). Onycophorans and Echiurans have a less pronounced, or partial segmentation of the body. The phylogeny is a broad consensus of molecular and morphological traits. Note that we have displayed a trichotomy of pancrustaceans, myriapods and chelicerates, as these relationships are contested. The branch lengths are arbitrary.