Loriano Ballarin (ORCID: 0000-0002-3287-8550) is a Professor of Zoology at the Department of Biology, University of Padova (Italy). He is a member of the editorial board of the Invertebrate Survival Journal and the European Journal of Zoology, and is a founding member of the Italian Association of Developmental and Comparative Immunobiology (IADCI). His main research interests are the evolution of innate immunity and the study of the cellular and molecular basis of immune responses in marine invertebrates, with particular reference to the role of hemocytes/coelomocytes in immune defense and, more generally, in the stress response. Most of his studies were carried out using the colonial ascidian Botryllus schlosseri as a model organism. His interest in stem cells is directly related to their role in hematopoiesis, as they assure the continuous renewal of the circulating immunocytes of marine invertebrates. He is the chair of the COST Action 16203 MARISTEM “Stem cells of marine/aquatic invertebrates: from basic research to innovative applications” that supported the publication of this book. He is the author or co-author of more than 130 peer-reviewed publications in scientific journals, co-editor of scientific books, including “Lessons in immunity: from single-cell organisms to mammals” (Elsevier, 2016), and guest editor of Special Issues, including: “Ancient immunity. Phylogenetic emergence of recognition-defence mechanisms” (Biology (Basel), 2020-2021).