How might a notochord have supported the earliest ancestors of jawless fishes?

The notochord served as a vital structural element for the earliest ancestors of jawless fishes (Agnatha), acting as a flexible, rodlike support that stiffened the body.12

By providing a turgid core and fibrous sheath, the notochord prevented the animal's body from shortening during the muscular contractions required for locomotion. This structural integrity allowed these early, soft-bodied organisms to produce effective swimming waves, facilitating movement through their aquatic environments. In addition to its role in physical support, the notochord played an organizational role in the development of the nervous system, a fundamental feature that persisted as these organisms evolved into more complex vertebrates.321