Evolution of the multicellular animals

Molecular sequence analysis is providing new insights into the study of met azoan relationships, The use of ribosomal RNA sequences is revising many of the metazoan phylogenies that have been established traditionally with ana tomical and embryological data. Four new findings that seem to be well supp orted by molecular data, both from the authors' laboratories and from other s, are described and discussed. First, the arthropods are members of a deep primary clade within the protostomes and are not the sister taxa of either the annelids or the mollusks, Second, the lophophorate animals are clearly protostomes and are contained within a lophotrochozoan superclade includin g the mollusks, annelids, and many other phyla. Third, the arthropods toget her with all other molting animals comprise a second monophyletic superclad e within the protostomes, the ecdysozoa, Fourth, the platyhelminthes are co ntained within the lophotrochozoan superclade.