All chordates share three key characteristics that define this diverse group of animals.
- Notochord: This is a flexible rod-like structure that provides support. In many chordates, the notochord is replaced by the vertebral column (spine) during development, but it is present during some stage of the life cycle in all chordates, including humans.
- Dorsal Hollow Nerve Cord: This is a tube-like structure located above the notochord that develops into the central nervous system, which includes the brain and spinal cord. It distinguishes chordates from other animal phyla, which typically have solid nerve cords.
- Pharyngeal Slits: These are openings that develop in the pharynx (the area behind the mouth) and are found in all chordates at some stage of development. In some species, they develop into gills in aquatic animals, while in others, they contribute to the structure of the neck and vocal apparatus in terrestrial animals.
These three characteristics are essential for classifying animals within the phylum Chordata and highlight the evolutionary relationships among various species.