The evolution of head appendages in marine bristle worms (annelids)

These appendages show an enormous variety of forms, from feather-like crowns in sabellids, paired long palps in spionids or countless fine appendages that can be admired on cirratulids. They play a key role in the evolution in the group of annelids, which comprises far more than 20,000 species. Despite their importance for the understanding of evolutionary relationships, terms like antenna, palp, branchae or cirrus are used rather arbitrarily in the technical literature, since there is simply no definition using uniform criteria, or existing systematizations are implemented incorrectly or even inconsistently. The aim now is to describe uniform morphological criteria for the doubtless identification of these head appendages and to detect the genes involved in their formation by in situ hybridization.

Methods: Immunohistochemistry and confocal Laser-scanning-microscopy (cLSM), electron microscopy (SEM, SBF-SEM), Azan-histology, µ-CT, 3D-reconstruction