The revision of the invertebrate phyla into the
Lophotrochozoa and the Ecdysozoa has raised the issue of
how often segmentation evolved in the animal kingdom.
– Until recently, the majority of biologists favored the
hypothesis that arthropods evolved from the
segmented annelids, or that both groups evolved from a
common segmented ancestor.
The molecular data would split these phyla into two
different parts of the animal phylogenetic tree.
This conflict has focused interest in the evolutionary
origin of segmentation