Morell, M., Lenoir, M., Puel, J., Jauniaux, T., Dabin, W., Ferreira, M., André, M. Describing odontocete inner ear ultrastructures: contribution from scanning electron microscopy Proceedings of the 24th Conference of the European Cetacean Society, Stralsund, Germany, 22nd to 24th of March 2010, p.102, Mar 2010 Abstract: The description of the cetacean auditory pathways morphology is a key conservation issue to assess the effects of acoustic pollution on marine ecosystems. Because odontocetes produce species-specific sounds at diverse frequency ranges, differences in echolocation signals could reflect morphological cochlear differences. One of the challenging steps after extraction and fixation of fresh ear samples from stranded individuals is to decalcify the bone envelope to access the cochlea without damaging the soft tissues. 111 ears from 13 different odontocete species stranded in the Mediterranean Sea, the North Atlantic and the North Sea were processed to build a decalcification protocol using the following solutions: RDO®, EDTA and EDTA in a microwave oven. Here, we show scanning electron microscopy images that reflect the presence of 1) outer hair cells in a fourth row at the first apical cochlea turn in Phocoena phocoena and 2) outer hair cells stereocilia prints in the tectorial membrane of Delphinus delphis, Phocoena phocoena and Stenella coeruleoalba. These ultrastructures have not yet been reported in the literature for these species. Project: eCREM, Effects and Control of Anthropogenic Noise in Marine Ecosystems