Phylum Chordata: The animal kingdom was divided into several major groups or phyla of animals. Here we will seen the what is phylum chordata and their general characters.
Phylum Chordata
Currently animals are divided into 30 phyla and last group of animal kingdom is called phylum Chordata. The name chordata was suggested by Balfour in 1880 and the name is derived from two Greek words i.e. Chorde means string or cord and ata means bearing. The characteristic feature of such animals are in the form of a stiff, supporting rod-like structure along the back, the notochord, which is found in all the members of the phylum chordata at some stages of their life. All remaining phyla of animal kingdom are often called ‘Non-chordate’or invertebrates’ because they have no notochord or backbone in their body structure.
Phylum Chordata is the largest group of animals in animal kingdom. It is the highest and the most important phylum comprising a vast variety of living and extinct animals including human himself. The today’s living chordates are familiar vertebrates animals divided into different classes or groups into fishes, amphibians, reptiles, birds and mammals. Besides, they include a number of marine protochordates.
The chordates exhibit different diversity of forms. There are about 49,000 species of chordates; on record which are only half in numbers of living species of mollusks and less than 1/10th those of arthropods. The protochordates subphyla claim for nearly 2,500 species. Whereas subphylum vertebrates includes 46,500 species of these; fishes with approximately 25,000 species. It is commonly assumed that amphibian species number about 2500, reptiles 6000, birds 9000 and mammals are 4500.
Despite their modest number of species, the chordates make a disproportionate contribution to the biomass of the earth. Nearly they are medium to large in size. The vertebrates are considerably large and many of them are largest in living animal e.g. gigantic blue whale(Balaenoptera musculus), measure 35 meters long and 120 tons in weight, is the largest known animal. The whale shark (Rhineodon typus) reaches a length of 15 meters and is the second largest vertebrate after whale. The smallest fish, found in Philippine is Goby (Pandaka) measured only 10 mm(1 cm) long.
Ecologically Chordates are most successful animal in animal kingdom. They are able to occupy most kind of animal habitats and are adapted themselves to more modes of life than any other group of animal. They are found in the sea, in freshwater, in the air, and on the all parts of land from the poles to the equator. Birds and mammals are able to survive in cold climate because they have a constant body temperature, something no other animals have.
All the chordates possess four unique and fundamental characteristics at some stages of their life history. These include;
1. A dorsal hollow or tubular nerve cord
2. A longitudinal supporting rod like notochord and
3. A series of pharyngeal gill slits.
4. Post-anal tail – This is an extension of the body beyond the anus. In some chordates, the tail has skeletal muscles, which help in locomotion.
The above three common features appear during early embryonic life of all the chordates. But all these three features rarely persist in the adult form. Often they are modified or even lost in the adult stages of higher chordates. The notochord disappears during development in most vertebrates, while the nerve cord and the pharyngeal gill clefts or their derivatives remain in the adult. All these three characters were probably characteristic feature of the ancestral chordates. They distinguish chordates from all other animals and appear toreveal their common ancestry.
General Characteristic of Phylum Chordata
- Chordates are aquatic, aerial or terrestrial. All free living with no fully parasitic forms.
- Body small to large, bilaterally symmetrical and metamerically segmented.
- A postanal tail usually projects beyond the anus at some stages and may or may not persist in the adult.
- Exoskeleton often present; well developed in most vertebrates
- Body wall triploblastic with three germ layers viz., ectoderm, mesoderm and endoderm.
- They are coelomate animals having true coelom, enterocoelic or schizocoelic in origin.
- A skeletal rod, the notochord present at some stages in life cycle.
- A cartilaginous or bony, living and jointed endoskeleton present in the majority of vertebrates
- Pharyngeal gill slits present at some stage of life. These may or may not be functional
- Digestive system complete with digestive glands.
- Blood vascular system closed type. Heart ventral with dorsal and ventral blood vessels. Hepatic portal system well developed.
- Excretory system comprising proto or meso or metanephric kidneys
- Nerve cord dorsal and tubular. Anterior end usually enlarged to form brain.
- Sexes separate with rare exceptions. ‘Phylum Chordata’
Conclusion
Phylum Chordata is the largest group of animals in animal kingdom. It is the highest and the most important phylum comprising a vast variety of living and extinct animals including human himself. The today’s living chordates are familiar vertebrates animals divided into different classes or groups into fishes, amphibians, reptiles, birds and mammals.