A neuron is a very fascinating cell. It is a cell that is specialized to detect changes in the environment, translate that environmental information into the language of membrane potential changes (electrical signals), and engage in long-distance communication by transmitting such electric signals to distant targets in a body. The key to this transmission is the synapse, where the axon of one neuron uses exocytosis to release neurotransmitters that can diffuse and bind to receptors on the dendrite of an adjacent neuron. In essence, the synapse is a ‘decision point’ for determining whether or not the signal will proceed. It is the synapse which confers immense plasticity and potential for control to the whole circuit.

We have just seen that at least one single-celled organism contains most of the calcium toolkit that would be exploited in the release of neurotransmitters. But what about the other side of the synapse?

Over a year ago, researchers found that the sponge, which has no nervous system and does not form neurons, contains most of the machinery needed to complete the synapse. According to this news article:

Considered among the most primitive and ancient of all animals, sea sponges have no nervous system (or internal organs of any kind, for that matter), notes Todd Oakley, assistant professor in the Department of Ecology, Evolution and Marine Biology at the University of California, Santa Barbara. But, he adds, they “have most of the genetic components of synapses.”
[..]
He, Oakley and the rest of the team listed all the genes known to be operative in synapses in the human nervous system. They then examined the sponge genome. “That was when the surprise hit,” said Kosik. “We found a lot of genes to make a nervous system present in the sponge.”

Thus is not surprising from the FLE perspective. On the contrary, this is the very type of data we would expect if neurons and nervous systems were front-loaded.
Also:

“We found this mysterious unknown structure in the sponge, and it is clear that evolution was able to take this entire structure and, with small modifications, direct its use toward a new function,” said Kosik. “Evolution can take these ‘off the shelf’ components and put them together in new and interesting ways.”

Yes, evolution works quite well if it has handy tools on the shelf whose fuinctional potential can be more readily exploited in a multicellular context. After all, evolution largely depends on the tools and material it is handed.
According to the research article itself:

“The data presented here support the presence of a proto-post-synaptic scaffold in the last common ancestor to all living animals. The presence of a large number of post-synaptic genes in the genome of demosponge Amphimedon, the nearly absolute conservation of binding domains and ligands between this sponge and animals with neurons, as well as the expression of a set of post-synaptic mRNAs in the same cell type, suggest the proto-post-synaptic scaffold existed as an assembled functional structure very early in animal evolution.”

Another way of putting this is as follows: if we rewound the tape of life just prior to the origin of metazoa, it would not be surprising to see neurons evolve all over again. The stage was set.

But the research paper also notes there are certain key synaptic genes missing from the sponge genome. This raises some interesing questions from an FLE perspective. As we sequence more genomes from other sponges and protozoa, we may find these other key components. Also, to what degree would this toolkit act as bait for fishing out the key genes (the mechanism of baiting is explained in The Design Matrix)?