C) Vertebral column. Other three options are essential chordate characters. And post anal tail also be a character. But post anal tail is not present in humans and apes, like this vertebral column in vertebrates. So these characters may vary accordingly.

Answer:

Chordates are a group of animals that possess a set of characteristics that distinguish them from other animals. These characteristics include a notochord, dorsal hollow nerve cord, pharyngeal gill slits, and a post-anal tail. However, one of these characteristics is not essential to be considered a chordate.

Vertebral column is not an essential chordate characteristic.

The vertebral column is a structure made of bone or cartilage, which runs along the dorsal side of the body. It encloses and protects the spinal cord, which is part of the nervous system. Although most chordates have a vertebral column, it is not an essential characteristic of the group.

Other essential chordate characteristics are:

1. Notochord: It is a flexible rod-like structure that runs along the dorsal side of the body. It provides support and allows for movement. In some chordates, such as humans, the notochord is present only during embryonic development.

2. Dorsal hollow nerve cord: It is a hollow tube-like structure that runs along the dorsal side of the body. It is derived from the ectoderm and develops into the central nervous system. In chordates, the dorsal hollow nerve cord is located above the notochord.

3. Pharyngeal gill slits: These are openings in the pharynx that connect the pharynx to the outside environment. They are used for filter feeding in some chordates, such as lancelets, and for respiration in others, such as fish.

4. Post-anal tail: It is a tail-like structure that extends beyond the anus. It is used for swimming and balance in aquatic chordates, such as fish.

In conclusion, the vertebral column is not an essential chordate characteristic. Chordates can exist without a vertebral column, but they must possess the other essential characteristics of the group.