C. elegans neurons are identifiable by name and their functions and connections are mapped in a connectome.

“And each neuron has a name, like you said. And not only does every neuron have a name, many of them, we know what they do. So there's a few cells that are sensory neurons that sense particular chemicals. In certain situations, we'll know that a chemical will be sensed just by one neuron. There are other motor neurons and interneurons and all of that. We know how many dopamine neurons there are, and serotonin neurons, and we know them all by their name. Not only that, we know how they are connected to one another. We have a map, a connectome since the 80s, like a subway map that tells us which neuron talks with which other neurons, and it is the same.”