Development of the circulatory system in Crustacea - Testing potential homologies between arthropods and annelids

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As a potential synapomorphy of Annelida and Arthropoda ¿segmentation¿ plays a central role in the current controversy Articulata versus Ecdysozoa. However, segmentation does not constitute a single character in a data matrix but a highly complex set of features, where the development of the circulatory system is one of the major components. Whereas in annelids, blood vessels appear between the epithelia of the developing coelomic cavities, it is more uncertain what occurs in euarthropods because putative ¿coelomic¿ cavities become transformed, divided and reduced. During the first phase of this project, the development of the circulatory system in three exemplar species of Crustacea ¿ representatives of Stomatopoda, Amphipoda and Decapoda ¿ will be studied. Stomatopoda possess the circulatory system with the highest degree of homonomy in comparison to all other arthropods and are in particular suited for a comparison with annelids. The representatives of Amphipoda and Decapoda are chosen because of already well established cultures and methodology. Based on serial sections, transmission-electron-microscopy, Micro-CT, single cell labelling visualised by confocal laser-scanning-microscopy, and finally 3D reconstruction using up-to-date software, the most detailed study of the development of the circulatory system to date will be carried out, providing the basis for a more substantial comparison with the development of the circulatory system in annelids. Detailed similarities between arthropods and annelids in both adult anatomy and development could provide support for the homology of segmentation, whereas a large number of differences might weaken the probability of homology.3