I don't have anything specific in mind that covers this (I'll look around), but maybe take a look at the work by Nicholas Strausfeld for some actual data on early nervous systems [0], and Leigh van Valen for the general theoretical framework [1].

0. https://scholar.google.com/scholar?q=Nicholas+Strausfeld

1. https://www.mn.uio.no/cees/english/services/van-valen/evolut...