Question

What are the five main characteristics of chordates?

Answer 1

Chordata:

1. These creatures have five basic traits: a notochord, a dorsal hollow (tubular) nerve cord, pharyngeal gill arches or slits, and a post-anal tail.

Notochord:

1. In all chordate embryos and some adult chordate species, the notochord is a flexible, rod-shaped mesodermal structure.
2. The notochord provides firm skeletal support as well as a flexible site for axial muscle attachment between the digestive tube and the nerve cord.
3. Throughout the life of some chordates, the notochord acts as the body's primary axial support.
4. The notochord, on the other hand, is only present during embryonic development in vertebrates (craniates), when it promotes the formation of the neural tube and acts as a support for the growing embryonic body.

Dorsal nerve cord:

1. The ectoderm that makes up the dorsal hollow nerve cord becomes a hollow tube as it develops.
2. Chordates have it dorsally to the notochord.
3. In vertebrates, the neural tube develops into the brain and spinal cord, which form the central nervous system (CNS).
4. The peripheral nervous system (PNS) refers to the nerves that run outside of the brain and spinal cord (including the cranial nerves).

Presence of pharyngeal gill slits:

1. Slits in the pharynx (the region right behind the mouth) that open to the outside world is known as pharyngeal slits.
2. Pharyngeal slits are seen in creatures that live in aquatic habitats and allow water to exit the mouth during feeding.
3. The pharyngeal slits are converted into gill supports in vertebrates and jaw supports in jawed fishes.
4. Slits are greatly changed into components of the ear, tonsils, and thymus glands in tetrapods (land vertebrates).

Post anal tail:

1. A posterior elongation of the body that extends beyond the anus is known as the post-anal tail.
2. In aquatic organisms like fishes, the tail contains skeletal structures and muscles that facilitate locomotion.
3. The tail also aids balance, courtship, and alerting when danger is approaching in some terrestrial vertebrates.
4. The post-anal tail in humans and other big apes is reduced to a vestigial coccyx ("tail bone") that aids in balance while sitting.