Much of the difference between the single-celled fungus and the two multicellular animals is accounted for by those genes and proteins that make multicellularity possible.
Nicholas Strausfeld, the study's author, highlights that no one was expecting to find a brain as advanced as this so early in the history of multicellular animals.
The university's Schaap laboratory studied a simple multicellular organism, Dictyostelium, in which motile cells (those which can move spontaneously) differentiate into two immobile cell types: stalk cells and spores.
He chose the worm because it was a multicellular animal with properly differentiated organs (a nervous system, gut and so on) that consisted of only a few hundred cells.