Detlev Arendt obtained his Ph. D. in zoology from the University of Freiburg, Germany in 1998. After three years pursuing a postdoc, he set up his own laboratory at the European Molecular Biology Laboratory in Heidelberg.   Detlev's main interest lies in the evolution of the animal central nervous system (CNS). He has compared nervous system development in insects and vertebrates, and in 1994 revived the idea of "dorsoventral axis inversion" : This concept implies that the last common ancestors of insects and vertebrates, Urbilateria, were already in possession of a CNS in its ventral body side, and that vertebrates subsequently turned upside down during their evolution, so that their present CNS is now located dorsally. In order to learn more about urbilaterian CNS development, and its anatomy, physiology, genes and molecules, his laboratory has established the marine ragworm Platynereis dumerilii as a novel molecular model system. This species exhibits many ancient features in its lifestyle, anatomy and development, and is a good approximation of the urbilaterian. In a bioinformatic comparison Platynereis shows an ancient gene inventory and ancient gene structure. Detlev and colleagues have characterised a special type of photoreceptor cell, a "ciliary photoreceptor" that, by molecular fingerprint comparison, relates to the rods and cones, the visual photoreceptors of the vertebrate retina. This has prompted the fascinating hypothesis that the vertebrate eye has evolved from within the urbilaterian brain. Besides ciliary photoreceptors, the Platynereis brain harbours sensory-neurosecretory cells that molecularly resemble cells situated in the vertebrate hypothalamus, but act in a simple and very different neurobiological setting. Detlev's goal is to elucidate the functioning of these cell types in the marine environment to gain insight into the evolutionary origins of the animal CNS.