One hundred years of research on the immortal jellyfish Turritopsis spp. from Japanese water, which can revert in miraculous fashion from the dying medusa to the young polyp stage, is reviewed. Almost all of the publications on the biology of Turritopsis written by the author and coauthors are reprinted here, including works that first appeared in books, newspapers, academic journals, and as handouts at public lectures held by various organizations. They are magnified or reduced from the original size, and sometimes modified from the original printing style. All the sources of the reprinted material are listed, together with major academic references cited in this book. An abbreviated curriculum vitae, profile, and contact information for the author are provided, together with a list of relevant internet homepage sites. In addition, articles on bivalve-inhabiting hydrozoans and Yawara medusa, Laodicea undulata, are included.