Tobias Lehmann

From EESwiki

Evolution of ocelli and optic lobes in Pycnogonida (Arthropoda): Fine structure and neuroanatomy

Pycnogonida have attracted peculiar attention of zoologists by virtue of their uncommon morphology and life. For quite a long time their phylogenetic position among arthropods was not clear, and thus they represented a classical taxon incertae sedis. Traditionally Pycnogonids are seen as a highly ancestral group derived quite early from the chelicerate stem lineage. Other results led to the idea that Pycnogonida might even been more ancestral, i.e. the sister group of all other extant Euarthropoda. This makes clear that Pycnogonida are a key group for the understanding of the phylogeny of the Arthropoda/Euarthropoda, and thus it is not surprising that some aspects of their neuroanatomy and segmentation were recently hotly debated, e.g. the assignment of the chelifores to the segments and neuromeres of the anterior body region. Among pycnogonid organs that might have a high impact in this connection, the visual system is certainly one of the most important, since it also provides key features and therefore deserves renewed attention. We seek to undertake a comparative analysis of the pycnogonid visual system on two levels: (1) Fine structural analysis of the eye quadruple of representatives of the major pycnogonid lineages according to their actual systematics, and (2) analysis of the visual neuropils of three “model” pycnogonids using neuroanatomical techniques. The scope of the project is to reveal the visual system’s sets of characters in the groundplan of Pycnogonida and thus contribute to reconstruction of the phylogeny of the most ancestral arthropod phyla.

Supervisor: Roland Melzer