A Trichoplax is a placazoan and quite primitive at that. The nervous system package remains unwrapped for a billion years:
Almost 10 years ago, Trichoplax’ genome was sequenced to investigate which genes it possesses.
This showed that Trichoplax possess one of the smallest genomes ever studied. Most surprisingly, however, it also turned out that Trichoplax possess virtually all the machinery needed to have a functioning nervous system.
But there is one problem: on closer inspection of Trichoplax under a microscope, there is no evidence that there are nerve cells.
But despite the lack of a nervous system Trichoplax is able to perform relatively quite complex behaviours.
Trichoplax, for example, can move, sense the presence of food, stop and devour algae, and sense gravity.
Thomas Lund Koch, “What is the point in having a nervous system?” at ScienceNordic
The cells communicate with each other via molecules, it seems.
Koch adds, “How the nervous system evolved is an interesting biological question that might give us a better understanding of how our own nerve cells are constructed.”
It’s almost like the nervous system is software that was never used, but that raises Forbidden Ideas, doesn’t it?