Annelida is considered the major sister phylum to Arthropoda. Both phyla share features of segmentation (metamerism) and were historically grouped in the clade Articulata. Molecular phylogenetics places both in the superphylum Ecdysozoa (with nematodes and others that moult) or relates them through the lophotrochozoa. Annelids and arthropods share ancient common ancestry of segmented body plans.