Using Cerebral Characters to Reconstruct Deep Metazoan Phylogeny: Comparative neuroarchitecture of the brain in annelids, molluscs and arthropods analyzed with confocal laser scanning microscopy

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Numerous anatomical features of the brain of arthropods are highly conserved during evolution, including the presence and basic neuroarchitecture of neuropils such as the central body and the mushroom bodies. These features are therefore ideal markers from which to derive phylogenetic relationships of arthropods with other major groups of the animal kingdom. While the literature on euarthropod brain architecture is abundant there have been only sparse and superficial reports examining the internal structure of cerebral ganglia of most other invertebrate phyla. In the beginning of “Deep Metazoan Phylogeny” we have analyzed in detail the neuroarchitecture of basal representatives of euarthopods and of onychophorans, resulting in a clearer picture of the ground pattern of the brain of panarthropods. We have investigated the cellular anatomy of several representatives of the Annelida, and during the second application period, of the Mollusca. The aim of the project is to compare the ground pattern of the arthropod brain to that of annelids and molluscs. The analysis of the annelid brain is in an advanced stage and will be supplemented by detailed investigations of brain centers of special interest. We will continue to investigate cerebral ganglia of basal molluscs, a group that is otherwise not covered by morphological projects within DMP. The use of immunofluorescence antibody techniques and state-of-the-art confocal laser scanning microscopy along with 3D-reconstructions will allow us to analyze the anatomical data in detail. Methodological consistency and strict criteria for identifying homologous brain structures will result in a comparable set of characters. Together with results from other members of DMP the acquired set of data will be subjected to a combined phylogenetic analysis in the concluding phase of DMP.