Rob Desalle: American Museum of Natural History, Division of Invertebrate Zoology, New York, USABernd Schierwater: ITZ, Ecology and Evolution, TiHo Hannover, Germany

• Introduction. A Phylogenomic Journey Through the Animal Tree of Life: Key Innovations in the Evolution of Metazoa. Tangled Roots in the Animal Tree of Life. Putting Animals in their Place Within a Context of Eukaryotic Innovations. Elucidating Animal Phylogeny: Advances in Knowledge and Forthcoming Challenges. Key Transitions in Animal Evolution: a Mitochondrial DNA Perspective. Pending Issues in Development and Phylogeny of Arthropods. The Earliest Animals: From Genes to Transitions. The Pre-nervous System and Beyond—Poriferan Milestones in the Early Evolution of the Metazoan Nervous System. A Key Innovation in Evolution, the Emergence of Neurogenesis: Cellular and Molecular Cues from Cnidarian Nervous Systems. From Cnidaria to "Higher Metazoa" in One Step. Basal Metazoan Sensory Evolution. Cnidarian Gene Expression Patterns and the Origins of Bilaterality—Are Cnidarians Reading the Same Game Plan as "Higher" Animals? Key Transitions During Animal Phototransduction Evolution: Co-duplication as a Null Hypothesis for the Evolutionary Origins of Novel Traits. Vertebrate Hox Genes and Specializations in Mammals. Pattern and Process at the Base of the Metazoan Tree of Life. Field Biology of Placozoans (Trichoplax): Distribution, Diversity, Biotic Interactions. Trichoplax and Placozoa: One of the Crucial Keys to Understanding Metazoan Evolution. A Food’s-Eye View of Animal Transitions. Lost in Transition: The Biogeochemical Context of Animal Origins. Redefining Stem Cells and Assembling Germ Plasm: Key Transitions in the Evolution of the Germ Line. Questions and Discussion.