Question

You are a chordate, yet you lack most of the main derived characters of chordates. Explain.

Short answer

There are four main traits that are present in all vertebrates but are present only at the embryonic stages in humans. The traits include the presence of the notochord, nerve cord, pharyngeal clefts, and the anal tail.

The notochord changes into vertebral discs, the nerve cord forms the spinal cord and the brain, the pharyngeal clefts form the other structures, and the tail completely disappears.

Step-by-step solution

Human embryonic development

Humans exhibit internal development of the fetus. The female carries the infant for nine months until all the body structures and organs are formed. During embryonic development, several structures are formed that disappear as the development progresses.

Notochord

The notochord in humans that is present during the embryonic stage gives rise to the discs found between the vertebrae. These discs act as shock absorbers and hence make the vertebral column strong. The discs help in allowing movement in the vertebral column.

Nerve cord

The nerve cord in humans is found during the embryonic stages. It is located on the dorsal side of the notochord. During the later stages, this nerve cord develops into the spinal cord.

Pharyngeal clefts

The pharyngeal clefts are important structures that are observed in all vertebrate organisms. These pharyngeal clefts are maintained in many marine organisms to facilitate the removal of water. However, in humans, these clefts are present only during the embryonic stages, and later on, they give rise to body structures.

Anal tail

The anal tail is a muscular tail that extends from the anus. This tail is less significant in humans hence is referred to as a vestigial organ. The anal tail disappears entirely during the course of development.