what is the difference between nerve card and notochord

Dorsal nerve cord is the embryonic feature of chordates that constitutes the central nervous system in them while ventral nerve cord forms the nervous system of some invertebrates. Nerve chord consists of a notochord, pharyngeal slits and post anal tail. 

Notochord is the chief distinguishing feature of Chordates, which is a dorsal longitudinally running rod. It lies between the dorsal nerve tube and the gut. It increases locomotory power and internal support. It probably evolved originally in the swimming larval forms of chordate ancestors. It still resembles something like its original form in few remaining group of non vertebrate chordates, but in most chordates it is mainly replaced during embryonic development by bony vertebrae of the vertebral column, or backbone

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