Cephalopod development: what we can learn from differences

Introduction The molluscan neuro-muscular system shows extreme diversity. Cephalopods present an original body plan, a derived neuro-muscular complex and a development with drastic changes in the anteroposterior/dorso-ventral orientation. How it took place during evolution is an unresolved question that can be approached by the study of developmental genes. Studying the expression of conserved transcription factors (Pax and NK families, otx, apt) and morphogen (hedgehog) during development is a good test of the conservation of their functions. We underline here unexpected expression patterns during cephalopod development, and we aim to suggest that these patterns may be, at least partly, in relation to morphological novelties in this clade. Conclusion The expression patterns observed point out the diversity of molecular pathways recruited during evolution and the necessary carefulness regarding generalization of results obtained from a very small set of model organisms. Studying different species, with a large diversity of morphology, could help to have a better understanding of the variety of the genes roles and/or of the plasticity of networks.