Characteristics of Chordata:

(i) Animals of Chordata, have a notochord in some stage of their life.

(ii) Animals have nerve chord on the mid­dorsal surface.

(iii) They have pharangeal gill clefts, at some stage of life.

(iv) The heart is present on the ventral surface

(v) Blood circulatory system is of closed type

This sub-kingdom is classified into five classes:

1. Class-Pisces: This class includes fishes and other aquatic animals. Fishes are aquatic and cold-blooded. Their body is spindle-shaped, divided into head, thorax and tail and their bodies are covered with scales. They have fins which help them in swimming. Endo-skeleton of fishes is cartilaginous or bony. Respiration takes place through gills. The heart is two-chambered.

Examples are: Dogfish, Rohu, Sea horse, Stingray etc.

2. Class-Amphibia: It includes many kinds of frogs. Animals can live both on land and in water. Their body is divided into head, thorax and abdomen. Their skin is smooth and wet, due to mucous. They have two pairs of legs, which help in swimming and locomotion. They respire through skin and lungs. Heart possesses two auricles and one ventricle.

Examples are: Frog, Toad, Tree frog, Salamander.

3. Class-Reptilia: It includes many kinds of snakes. Animals of this class crawl (creep), on the ground.Animals of this class respire through the lungs. Their body is divided into four parts – Heart, neck, thorax and tail and covered by endodermal scales. Their heart has two auricles and one incompletely divided ventricle. Animals of this class lay eggs.

Examples are: Tortoise, Lizard, Flying lizard, Viper, Chamaleon.

4. Class – Aves: This class includes a different kind of birds, that can fly in the air.
Their fore limbs are modified into wings, which help them in flying. Their body is boat shaped and stream­lined, divided into head, neck, thorax and tail, covered by feathers. There are no teeth in their jaws. They have horny beak. Their bones are hollow, with air-filled cavities. They have two pairs of pentadactyl (five digits) limb.

Examples are: Pigeon, Crow, Sparrow, Ostrich.

5. Class – Mammalia: It includes big animals, like Kangaroo, bat, monkey, cow and man. Developed mammary glands are found in females, mothers feed milk to young ones, through mammary glands. Their body is divided into head, neck, thorax and tail. Hairs are present on the body. Ear pinnae (External ear) is present. They are warm-blooded.

They respire through the lungs. The heart is completely four-chambered. Heart has 2 auricles and 2 ventricles. Most of the mammals are viviparous.

Examples are: Bat, Man, Mongoose, Rat, Lion, Tiger.