The central nervous system of velvet worms (Onychophora) - Shedding light on the evolution of the panarthropod brain

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Arthropods, arguably the most successful animals worldwide, have fascinated researchers for centuries due to the complexity of their bodies. One of the most important features of the arthropod body is their nervous system, which reflects the anatomical complexity to a great extent. Understanding the evolution of these puzzling organs requires investigations of both arthropods themselves and their closest relatives - Onychophora (velvet worms) and Tardigrada (water bears), which all together compose the Panarthropoda. As sister group to either tardigrades plus arthropods or arthropods alone, onychophorans play a key role for understanding the evolution of morphological traits within panarthropods. Nevertheless, despite their significant phylogenetic position, their nervous system, in particular the brain, is largely understudied. Therefore, the aims of the proposed project are to (i) clarify existing controversies surrounding the nomenclature and presumptions of putative homologies of the onychophoran brain to that of arthropods, and (ii) characterise numerous undescribed structures and features of the onychophoran brain. On the basis of 3D reconstructions of synchrotron radiation-based X-ray micro-computed tomographic and nanofocus X-ray source tomographic data sets - in addition to a wide range of neuroanatomical methods, such as a variety of antibody labelling and neuronal tracing - a three-dimensional "atlas" of the onychophoran brain will be designed. Moreover, this study will illuminate the onychophoran brain beyond morphological characters and, in addition, investigate potential neurogenesis in adult onychophorans, a feature so far unknown for these animals. Furthermore, the development of distinct brain regions will be examined as this will yield invaluable evidence for the origin of cerebral structures and, therefore, will help to draw putative homologies to arthropods. The obtained data will be valuable not only for understanding the anatomy of the onychophoran brain itself but, in addition, for elucidating the evolution of the anterior part of the central nervous system in panarthropods. The obtained results will therefore largely contribute to our understanding of the evolution of the intriguing arthropod nervous systems.