Figure 1

Phylogenetic relationship among segmented and unsegmented phyla. Phylogeny of bilatarians based on [14]; segmented and pseudosegmented animals identified after [7, 12, 13]. (A) Segmented phyla (yellow stars) are more closely related to unsegmented phyla than to each other. (B) Segmentation is no longer a rare characteristic if both segmented and pseudosegmented phyla are considered (red stars mark groups identified as segmented or pseudosegmented in several papers, orange stars mark groups identified as segmented or pseudosegmented in one paper and unsegmented in another). Here, ‘pseudosegmented’ is meant solely to distinguish traditionally segmented chordates, arthropods and annelids from other phyla with repetition of units with anterior-posterior polarity along the anterior-posterior axis. It does not necessarily mean that there is a biological distinction between these groups based on their repeated units.