Question

discuss the main features of Chordates and give at least three examples of organisms that belong to the phylum Chordata.

Answer 1

Answer:

Chordates exhibit the following characters. All chordates exhibit four fundamental characters. They are notochord, dorsal nerve cord, pharyngeal gill slits and post anal tail, at least at some stage of their life.

1. Notochord:

It is a stiff elastic mid dorsal longitudinal rod lying between the nerve cord and alimentary canal. It is derived from the embryonic chordamesoderm. It is made up of a core of vacuolated cells surrounded by an inner sheath of fibrous connective tissue and outer sheath of elastic connective tissue. It is a skeletal or supporting structure present in the embryonic stages of all chordates. It persists throughout life in Amphioxus and vertebrates like cyclostomes. In vertebrates, the notochord is replaced by vertebral column. In mammals, notochord is in the form of vestigeal swellings in the vertebral column. They are called Nuclei pulposi

2. Dorsal Tubular Nerve cord:

The nerve cord in chordates is a single hollow tubular structure, situated dorsal to both the alimentary canal and notochord. It is derived from embryonic neurectoderm. In higher chordates, the nerve cord is differentiated into an anterior brain and a posterior spinal cord.

3. Pharyngeal Gill-Slits

These are paired perforations present on each side of the pharynx leading to the exterior. Gills are situated in pharyngeal slits. Gill slits are derived from ectoendoderm. Gill slits may be retained throughout life as in protochordates, fishes and some amphibians and help in respiration. In Reptiles, Aves and Mammals, only non functional, externally closed pharyngeal slits appear during embryonic stage

4. Post anal Tail

Tail of chordates is post anal. It is the posterior elongation of the body extending beyond the anal opening or cloaca. It is reduced or absent in some adults. Tail has no coelom and viscera, but has muscles, nerve cord and notochord.

Ex: Fish, frog, snake, bird and human