Ctenophora (comb jellies) are animals but they have very strange nervous systems: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4334147/ https://www.ncbi.nlm.ni

Ctenophora (comb jellies) are animals but they have very strange nervous systems: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4334147/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4334147/ "Finally, metabolomic and pharmacological data failed to detect either the presence or any physiological action of serotonin, dopamine, noradrenaline, adrenaline, octopamine, acetylcholine or histamine – consistent with the hypothesis that ctenophore neural systems evolved independently from those in other animals."