Fig. 4.

Schematic phylogeny of the evolution of neuronal polarity. The evolutionary relationships of key groups of animals with nervous systems are shown. These relationships are based on recent sequence analysis (Ryan et al., 2013; Moroz et al., 2014). We argue that at least a minimal AIS-like domain is likely to be present in all bilaterians including ecdysozoans like Drosophila and C. elegans and lophotrocozoans like leech and Aplysia. Polarized microtubules in axons and dendrites are also found in different bilaterian branches. It is currently an open question whether these key features of polarized neurons are found in cnidarians and ctenophores.