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InhaltsangabeThe Question of Metazoan Monophyly and the Fossil Record.- 1 Introduction.- 2 The Rise of Metazoans.- 2.1 Are Metazoans Monophyletic?.- 2.1.1 Primitive Metazoans.- 3 Fossil Evidence for the Early Evolution of Metazoans.- 4 The Search for Pre-Ediacaran Metazoans.- 5 Where Do We Go from Here?.- 5.1 What is the Sister Group (or Sister Groups) of the Metazoans, and Will the Fossil Record Yield any Insights?.- 5.2 What Are the Inter-Relationships of the "Primitive" Metazoans, Notably the Sponges, Cnidarians, and Perhaps the Ctenophores?.- 5.3 Metazoan Evolution and Convergence: What Are the Constraints?.- References.- The Evolution of the Lower Metazoa: Evidence from the Phenotype.- 1 Introductionn.- 2 Origin of Multicellular Organization.- 3 Organization, Life Cycle and Lifestyle of the Ancestral Metazoa.- 4 The Origin of the Diploblastic Eumetazoa.- 4.1 Structural Innovations of the Eumetazoa.- 4.2 Models for the Most Primitive Organism with Diploblastic Organization.- Conclusions.- References.- Origin and Phylogeny of Metazoans as Reconstructed with rDNA Sequences.- 1 Introduction.- 2 Data and Methods.- 3 Theoretical Considerations: Sources of Errors in Phylogeny Inferrence.- 3.1 Species Errors.- 3.2 Character Errors.- 3.3 Algorithm Errors.- 3.4 Other Sources of Error.- 4 The rDNA Molecules.- 5 The Utility of rDNA Sequences Depends on Their Information Content.- 6 Monophyly of Metazoans.- 7 Relationships of Larger Groups of Metazoans.- 8 Determination of the Phylogenetical Signal Conserved in 18S-rDNA Sequences.- 9 Discussion.- References.- Sponges (Porifera) Molecular Model Systems to Study Cellular Differentiation in Metazoa.- 1 Introduction: Constituent Characters of Metazoa.- 2 Porifera and the Origin of Metazoan Evolution.- 3 Reproduction in Porifera.- 3.1 Sexual Reproduction: Gametes.- 3.2 Asexual Propagation.- 3.2.1 Gemmules.- 3.2.2 Buds.- 3.2.3 "Primordial Buds".- 4 Telomerase.- 4.1 Telomerase Assay.- 4.2 Telomerase Activity in Tissue from S. domuncula.- 4.3 Telomerase Activity in Tissue from G. cydonium.- 4.4 Telomerase Activity in Cells from G. cydonium.- 4.5 Comparison of Telomerase Activity Between Sponges and Mammalian Tumor Cells.- 5 Control of Cell Homeostasis in Sponges: Apoptosis.- 5.1 Induction of Apoptosis in Sponges.- 5.1.1 Cadmium-Induced Apoptosis.- 5.1.2 Induction of Apoptosis by Feeding the Animals with E. coli.- 5.2 Gemmule Formation.- 5.3 Induction of Expression of SDMA3 Gene.- 5.4 Telomerase Activity in Tissue from S. domuncula in Response to the Apoptotic Stimuli.- 6 Conclusion.- 6.1 Marker: Telomerase.- 6.2 Marker: Apoptosis.- 6.3 Shift from Immortal to Senescent Cells: Telomerase Activity as a Marker.- References.- The Notion of the Cambrian Pananimalia Genome and a Genomic Difference that Separated Vertebrates from Invertebrates.- 1 Introduction.- 2 Cyanobacteria in the Archean Ocean.- 3 Archaezoa as the First Animal in the Early Anaerobic Environment?.- 4 The Acquisition of Mitochondria Derived from an Endosymbiotic Paracoccus-Like Purple, Nonsulfur Bacterium as a Conditio Sine Qua Non to the Cambrian Explosion.- 5 Ediacaran Emergence of Porifera and Cnidaria as a Prelude to the Cambrian Explosion.- 6 Animals of the Cambrian Explosion and the Simultaneous Emergence of Three Subphyla of the Phylum Chordata.- 7 Genes in the Cambrian Pananimalia Genome.- 7.1 Pax 6 Genes and Eye Formation.- 7.2 The Universal Control of Anterior-To-Posterior Body Segment Differentiation by a Closely Linked Set of Hox Genes.- 7.3 The Antiquity of Ftz-F1, COUP and Other Genes Encoding Nuclear Receptor Proteins.- 8 Two Successive Rounds of Tetraploidization Events at the Beginning of Vertebrate Evolution and the Invariable Presence of Tetralogous Genes in the Vertebrate Genome.- 8.1 Four Sets of Hox Genes on Tetralogous Regions of Human Chromosomes 7pl2, 17q11.2-12, 12q13 and 2q34.- 8.2 Inevitable Degeneration of Tetralogous Genes to Trilogues, Dilogues and Even to Monologues.- 8.3 Tetralogues, Trilogues and Dilogues that