The amphioxus has a head, but it is so modest that you'd hardly know it was there. Lacalli and Holland have now done the same job on specimens of the salp Thalia democratica . Baby salps have a rudimentary hollow nerve cord that shortens and bunches up into a globular 'brain'. Later, a single eye appears on top of the brain, like a cherry on a cake. Detailed comparison of the salp brain with that of the amphioxus and vertebrates suggests that it corresponds with the mid-section of the vertebrate brain, involved in visual processing, and the source of some motor neurons.
Salps are arguably the most primitive living chordates.