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How does a notochord support a chordate’s body?

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A translucent X-ray fish (Pristella maxillaris) swims in an aquarium, showing its visible backbone and internal structures through its body. — Chordate X-ray fish (*Pristella maxillaris*), is an example of a chordate with a visible backbone.

The notochord serves as the primary longitudinal structural element for members of the phylum Chordata. It functions as a flexible, rodlike support structure that provides essential rigidity to the body.1

In organisms such as amphioxus, the notochord extends along the entire length of the body, where it is encased in a firm sheath. Its core contains muscle fibers that help maintain the stiffness of the rod. This structural support is critical during locomotion; by resisting compression, the notochord prevents the animal's body from shortening while it swims. This allows the musculature to pull effectively against the body's length, facilitating efficient side-to-side movement.2

In vertebrates, the notochord plays an organizational role during early development. As the animal matures, it is typically replaced or incorporated into the vertebral column, where it persists as the nuclei pulposi of the intervertebral discs, providing cushioning between the vertebrae.1