If there is any chance of us meeting intelligent aliens then it has to be that nervous systems can evolve more than just once (here). It's possible that we have found a separate evolution of a nervous system here on Earth.
The comb jellies (Ctenophora) are jellyfish-like animals that swim by the use of beating hair - cilia - rather than pulsating their bodies as jellyfish do.
The classification of the Ctenophora has recently changed, and it now looks like comb jellies are unrelated to any other animal that has nerve cells. If this is true, it's possible that the nerve cells in comb jellies evolved completely independently. This would mean that nervous systems are not unique and the likelihood of alien organisms with at least complex behaviour is greatly increased.