CBSE Class 9 Answered

Nerve cord is the dorsal tubular cord of nervous tissue above the notochord of a chordate that comprises or develops into the central nervous system. Notochord, on the  other hand, is a longitudinal flexible rod of cells that in the lowest chordates (as a lancelet or a lamprey) and in the embryos of the higher vertebrates forms the supporting axis of the body.

Nerve chord lies above the notochord. Nerve chord connects the brain to the major muscles and organs of the body.  In vertebrates, the backbone is deposited around the notochord and nerve cord.

Radial symmetry is a body plan in which all body parts of an organism are arranged around a central point.  Bilateral symmetry on the other hand is a basic body plan in which the left and right sides of the organism can be divided into approximate mirror images of each other along the midline.

Radial symmetry has several planes of symmetry whereas bilateral symmetry has only one plane of symmetry.