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The presence of major classes of transmitters in five basal metazoan lineages. The diagram shows the unrooted metazoan tree with hypothetical events of neuronal origins and the occurrence of other integrative systems together with representative types of feeding. See the text for details. Abbreviations: 5-HT, serotonin; DA, dopamine; NO, noradrenaline; A, adrenaline; OA, octopamine.
