The evolution of animal diversity is strongly affected by the origin of novel cell and tissue types and their interactions with each other. Understanding the evolution of cell types will shed light on the evolution of novel structures, and in turn highlight how animals diversified. Several cell types may also have been lost as animals simplified - for example did sponges have nerves and lose them? This book reveals the interplay between gains and losses and provides readers with a better grasp of the evolutionary history of cell types. In addition, the book illustrates how new cell types allow a better understanding permitting the discrimination between convergence and homology.

Andreas Hejnol is Professor and research group leader of "Comparative

Developmental Biology" at the Department of Biological Sciences (BIO) in Bergen,

Norway. After earning his Ph.D. in Comparative Zoology from the Free University

Berlin, Germany in 2002, he worked as a postdoctoral fellow in the laboratory of

Ralf Schnabel in Braunschweig and at the Kewalo Marine Laboratory in the lab

of Mark Q. Martindale in Hawaii. He led a research group at the Sars Centre from

2009-2019. His research aims to understand the evolutionary origin and diversification

of animal body plans, cell types, and organ systems. He is an ERC Consolidator

Grant holder and received for his achievements in Evolutionary Developmental

Biology and Comparative Zoology the prestigious Alexander O. Kovalevsky Medal

from the St. Petersburg Society for Naturalists in 2018.

Sally P. Leys is Professor in the Department of Biological Sciences at the University

of Alberta, in Edmonton, Canada. She earned her Ph.D. from the University of

Victoria under George Mackie in 1996, for which she received the Canadian Society

of Zoologists Cameron Award 1997. She held a Commander C Bellairs Postdoctoral

Fellowship from McGill University for postdoctoral research in Barbados (1997)

and then won an NSERC PDF which she took to the University Aix Marseille,

France (1998) and later to the University of Queensland, Australia (1998-2000). She

won an NSERC Women's University Research Award in 2000 and was Assistant

Professor (Limited Term) at the University of Victoria, British Columbia. In 2002,

she was awarded a Canada Research Chair Tier II at the University of Alberta in

"Evolutionary and Developmental Biology." Her research interests broadly concern

understanding the origin of multicellularity in metazoans and more specifically the

cellular and molecular basis of coordination in non-bilaterian animals, sponges,

ctenophores, placozoans, and cnidarians.