Comparisons of life-cycles of entoprocts, ectoprocts and phoronids indicate that the ectoprocts probably have evolved from entoproct-like ancestors, whereas the phoronids are of a quite different type. A review of our knowledge of structure and development of the three groups lends support to this idea. The Entoprocta and Ectoprocta should accordingly be united into the phylum Bryozoa, which is related to the Annelida and Mollusca. The Phoronida are probably more related to the deuterostomes.