Organisms that have a notochord but only for a specific period of their life cycle are called?

Organisms that have a notochord only for a specific period of their life cycle are called "chordates." Chordates are a group of animals that are defined by the presence of a notochord, which is a flexible rod-like structure that provides support for the body.

In some chordates, such as the lancelets and tunicates, the notochord persists throughout their entire life cycle. However, in other chordates, such as some species of fish and amphibians, the notochord is present only during their embryonic development and is later replaced by a vertebral column composed of individual vertebrae. These organisms are still considered chordates because they possess a notochord at some point in their development.