Nervous system evolved only once, about 3 billion years after life started, and nothing analogous to it ever evolved in any other lineage. [Urbilaterian]
From Science, July 3 2009, p. 24-26, “On the origin of the nervous system”:
Assembling these components into a cell a modern neuroscientist would recognize as a neuron probably happened very early in animal evolution, more than 600 million years ago… Scientists also disagree on which animals were the first to have a centralized nervous system and how many times neurons and nervous sytems evolved independently … [Leonid Moroz:] “Neurons may have appeared in multiple lineages in a relatively short time.”
p. 26:
If the bilaterian ancestor had a diffuse nervous system, centralized nervous systems must have originated multiple times in multiple bilaterian lineages… On the other hand, if the ancestor had a centralized nervous system, several lineages… must have later reverted to a diffuse nervous system. … Most researchers now agree that equally complex—but anatomically different—brains have evolved in birds, mammals, and other animal lineages, Northcutt says: “At least four or five times independently, … major radiations of vertebrates have evolved complex brain structure.”
From Science, July 3 2009, p. 24-26, “On the origin of the nervous system”:
p. 26: