What is a nerve chord?

A nerve chord is a solid or ganglionated longitudinal nerve cord located medially and ventrally between the digestive tube and notochord of lower invertebrates (animals lacking a backbone). For example, it is found on the ventral side of sea squirts (tunicates).

The nerve chord of tunicates contains the dorsal-root ganglia from sensory neurons while ventral horns with cell bodies for motor neurons occur only in vertebrates.