How does the cephalochordate nervous system compare with the vertebrate nervous system?

The cephalochordate nervous system shares a common ancestry with the vertebrate nervous system, evidenced by their shared dorsal hollow nerve cord and segmentally repeated nerves that supply body segments known as myotomes.123

However, the two systems differ significantly in complexity and specialization:

• Brain Development: While cephalochordates possess a main nerve cord with a slight anterior swelling, it barely qualifies as a brain. In contrast, vertebrates have a well-developed, greatly enlarged brain that is subdivided into functionally specialized regions.41
• Sensory Organs: Cephalochordates utilize simple pigment spots and light receptors within the nerve cord to detect changes in light intensity and direction. Vertebrates possess far more elaborate and complex sensory organs, such as advanced eyes.14
• Structural Organization: In both groups, sensory and motor fibers leave the nerve cord via dorsal and ventral roots. In cephalochordates and lower vertebrates, these roots remain separate, whereas in higher vertebrates, they typically unite into a single spinal nerve.2

Overall, the cephalochordate nervous system represents a primitive condition, while the vertebrate system exhibits advanced centralization and cephalization.2