Fig. 2

Phylogenetic tree of JFs evolution. Grey images represent representative species. The representative morphology of each animal JF is shown with a schematic diagram. The green dots represent critical events in the evolutionary history of JF. Protosynaptic proteins emerged in the Choanoflagellates and Spongia; the first NMJ emerged in the Annelida; glial cells participated in the NMJ structure in the Mollusca and Arthoropods; the first JFs of post-membrane depression emerged in the Chaeogmaths and Chordata; deeper and branched JFs were found in the Cartilagineous and Teleost fish; higher densities of JFs was found in Amphibians; the most complex of JFs structure existed in the mammalian animals