Stem Cells: Autonomy Interactors that Emerge as Causal Agents and Legitimate Units of Selection.- Putative Stem Cell Origins in Solitary Tunicates.- Cnidarian Interstitial Cells: The Dawn of Stem Cell Research.- Stem Cells in Aquatic Invertebrates: Common Premises and Emerging Unique Themes.- Stem Cells in Asexual Reproduction of Marine Invertebrates.- Neuroimmune Chemical Messengers and Their Conservation During Evolution.- Regenerating Echinoderms: A Promise to Understand Stem Cells Potential.- Secondary Mesenchyme Cells as Potential Stem Cells of the Sea Urchin Embryo.- Cell Dynamics in Early Embryogenesis and Pluripotent Embryonic Cell Lines: From Sea Urchin to Mammals.- Regeneration in Hemichordates and Echinoderms.- Stem Cells in Sexual and Asexual Reproduction of Botryllus schlosseri (Ascidiacea, Tunicata): An Overview.- Stem Cells, Chimerism and Tolerance: Lessons from Mammals and Ascidians.- Effect of Bacterial Infection on Stem Cell Pattern in Porifera.- Defence Mechanisms and Stem Cells in Holothuria polii and Sipunculus nudus.