1. Notochord: A notochord is a flexible, rod-like structure that runs along the dorsal (back) side of the animal. It provides support and flexibility, and it is present during the embryonic stage of all chordates. In some chordates, the notochord persists throughout life, while in others, it is replaced by a bony vertebral column.
2. Dorsal Nerve Cord: A dorsal nerve cord is a hollow, tube-like structure that runs along the dorsal side of the animal, above the notochord. It functions as the central nervous system, controlling and coordinating the activities of the body.
3. Pharyngeal Slits: Pharyngeal slits are openings in the pharynx, which is the cavity behind the mouth. These slits allow water to flow in and out of the pharynx, facilitating respiration and feeding. In some chordates, pharyngeal slits persist throughout life, while in others, they are modified or lost during development.
4. Post-Anal Tail: A post-anal tail is an extension of the body that extends beyond the anus. It is present during the embryonic stage of all chordates, but it may be reduced or lost in some adults. The tail provides balance and stability, and it may also serve as a storage site for fat and nutrients.