Having in hands an extensive knowledge of neuropeptide and GPCR repertoires in the four selected species (WP1), phylogenetic studies is carried out on neuropeptide and GPCR encoding genes. This analysis is made it possible to reveal the phylogenetical relationships between the newly characterized sequences and those already known in other species, advantage of the increasing number of available metazoan genomes in databanks. Such a phylogenetic scrutiny allow to build evolutionary scenarii on the neuropeptidergic systems. Most of the neuropeptides as well as their receptors are shown to belong to multigenic families. Until now, these families are mainly studied in arthropods and vertebrates. In non-vertebrate species, we focus on lophotrochozoans, to reinforce the investigations at the level of all the bilaterians. In the eel, as representative of vertebrates, we focus on the impact of the whole genome duplications (which were 3 in teleosts). We also include data from diploblastic metazoa, especially cnidaria, as some neuropeptide and GPCR families may have an early origin, before the emergence of the bilateria.