9623453 Martindale This research explores the molecular mechanisms behind the evolution of form in segmented animals. Many animals, including vertebrates and arthropods, are segmented. The polychaete marine annelids are an ideal model system to study how similar segments become different through evolution because of the great diversity in segmental morphology between closely related species. A family of genes known to control these segmental differences are the homeobox, or Hox, genes. This study will compare the deployment of these genes in two different species of polychaetes to look for evidence of changes that can explain the evolution from a simple repeated series of segments to series of segments that vary within the same animal. Information on the way the Hox genes operate in the polychaetes will add to our knowledge of how the Hox genes, and their regulation, have affected the evolution of developmental patterns within and between the major animal groups.