How is the design of a crayfish's nerve cord different from the design of a vertebrate's nerve cord?

The vertebrate nerve code is found dorsally while that of the crayfish is located ventrally of its body. Additionally, the ventral nerve cord of the crayfish is a solid ventral tube while that of the vertebrate is a hollow tube. All vertebrates are chordates, the dorsal nerve cord develops into nervous tissue of the brain and spinal cord; unlike the notochord which is the scaffolding for development of the bone and cartilage of the vertebral column. In the crayfish, they have a ventral nerve cord which is a collection of nerves found in the abdomen.