List the five characteristics common to all chordates.
The correct answer and explanation is :
Five Characteristics Common to All Chordates
All chordates (phylum Chordata) share five key characteristics at some point in their life cycle:
- Notochord – A flexible, rod-like structure that provides support and is present in the embryonic stage of all chordates. In vertebrates, it is replaced by the vertebral column during development.
- Dorsal Hollow Nerve Cord – A tube-like structure located dorsally (along the back), which develops into the brain and spinal cord in vertebrates.
- Pharyngeal Slits or Pouches – Openings in the throat region that serve various functions, such as filter-feeding in invertebrate chordates and gill formation in aquatic vertebrates. In terrestrial vertebrates, they develop into structures like the Eustachian tubes in humans.
- Post-anal Tail – A tail that extends beyond the anus, present in embryos of all chordates and retained in some adult species for movement and balance.
- Endostyle or Thyroid Gland – A structure involved in filter-feeding in primitive chordates that later evolves into the thyroid gland in vertebrates, playing a role in metabolism.
Explanation
Chordates are a diverse group of animals that include vertebrates (fish, amphibians, reptiles, birds, and mammals) and invertebrate chordates like tunicates and lancelets. These five characteristics define the phylum and appear at some stage of development. The notochord serves as the primary skeletal support in early development and is later replaced by the vertebral column in higher chordates. The dorsal hollow nerve cord is unique to chordates and develops into the central nervous system. Pharyngeal slits are crucial for respiration in aquatic species and adapt to different functions in land animals. The post-anal tail aids in locomotion in many species. Lastly, the endostyle/thyroid gland is involved in feeding and hormonal regulation. These features provide insight into the evolutionary links between simple chordates and complex vertebrates.