The Evolution of Ctenophore Brains[no description provided]
From his very first experiments, he could see that these animals were unrelated to jellyfish. In fact, they were profoundly different from any other animal on Earth.
Moroz reached this conclusion by testing the nerve cells of ctenophores for the neurotransmitters serotonin, dopamine and nitric oxide, chemical messengers considered the universal neural language of all animals. But try as he might, he could not find these molecules. The implications were profound.
Read "Aliens in our midst" at Aeon.