Lacalli (1996) suggested a scenario in which the ancestor had a single opening to the digestive system, and that the neural and non-neural mouths arose independently in protostomes and chordates, respectively.
Lacalli (1996) suxeriu un escenario no cal o antepasado tiña unha soa abertura no sistema dixestivo, e que as bocas neural e non neural se orixinaron independentemente nos protóstomos e cordados, respectivamente.