1. Possession of a Notochord: One of the defining features of chordates is the presence of a notochord. This flexible, rod-like structure runs along the dorsal side of the body and provides support and flexibility. It is a defining characteristic that distinguishes chordates from other animal groups.
2. Dorsal Nerve Cord: Another essential feature of chordates is the dorsal nerve cord. This neural structure is located above the notochord and is responsible for coordinating the body's activities. It is the precursor to the spinal cord in vertebrates.
3. Pharyngeal Slits: During their embryonic development, chordates possess pharyngeal slits. These slits connect the pharynx to the outside environment and serve various functions, including feeding and respiration. In some chordates, they may be retained in adults, while in others, they develop into specialized structures like gill slits or Eustachian tubes.
4. Post-Anal Tail: At some stage of their life cycle, chordates have a post-anal tail. This is a muscular extension that projects beyond the anus. In some chordates, such as tunicates, the tail may be present only during larval stages, while in others, like fish, it persists in adulthood.
5. Endostyle or Thyroid: Chordates possess an endostyle or thyroid gland. The endostyle is a mucus-secreting structure located in the floor of the pharynx and plays a role in trapping and filtering food particles. In vertebrates, it develops into the thyroid gland, which regulates metabolism.
6. Closed Circulatory System: Most chordates have a closed circulatory system, meaning the blood is confined within vessels. This advanced circulatory system allows for more efficient transport of oxygen and nutrients to body tissues and organs.
7. Segmentation: Chordates exhibit segmentation in their body structure. Their bodies are divided into repeating segments, each with its own set of muscles and nerves. This segmentation allows for greater flexibility and coordinated body movements.
8. Cephalization: Chordates display a high degree of cephalization, meaning the concentration of sensory organs and nerve centers in the head region. This feature enables more complex sensory processing and coordination of bodily functions.
The combination of these features, including the presence of a notochord, dorsal nerve cord, pharyngeal slits, and other advanced characteristics, sets chordates apart from other animal groups and positions them as the highest and most advanced group of animals.