The answer is arthropods have had more time to co-evolve with land plants than have vertebrates. Analysis of genes shows that their sequences are quite similar, and these sequences differ from those of the lophotrochozoans and deuterostomes. Between the annelids and arthropods will probably be viewed, in retrospect, as an instance of an evolutionary relationship that modern scientists had ʺset in stone, ʺ now having crumbled.