Animals can be broadly distinguished into two major groups the nonchordates (or invertebrates) and the chordates.Invertebrates account for more than 95% of the animal species that have been identified. These are animals which do not have a vertebral column or a back bone.
Pheretima posthuma is a common species of earthworm found living in burrows made in moist soil. It is nocturnal in habit.
External Features : Perplaneta americana is one of the several species of cockroaches that inhabit our country. Generally cockroaches are among the most common house hold insects.
The frog is generally considered as a typical vertebrate animal. It is an amphibious animal capable of living both in water and on land. However, it spends most of the time in its aquatic habitat such as ponds, pools and ditches.
Frog, being a typical vertebrate, shows the presence of a skeletal system that forms the internal supporting framework for the body. It can be distinguished into an axial skeleton and an appendicular skeleton. Axial skeleton consists of skull, vertebrae and sternum. Appendicular skeleton consists of the girdles (pectoral and pelvic) and the limb bones.
It consists of a pair of lungs, a pair of bronchi and a trachea. The lungs contain numerous microscopic functional units called alveoli.
The rat is a typical mammal. It is a nocturnal, household pest. It is normally found living in crevices and burrows. The rat has an elongated body which can be distinguished into a head, a trunk and tail.
The skeleton of rat has 223 bones that are distributed into the axial skeleton and the appendicular skeleton. The axial skeleton consists of skull, vertebral column, sternum, ribs and ear ossicles. The appendicular skeleton is represented by girdles and limb bones.
Lungs are the respiratory organs. The passage way for air is formed by external nostrils, pharynx, larynx, trachea and bronchi. Lungs contain large number of minute alveoli in which external respiration takes place. Surrounding the lungs and the heart is a thoracic cage containing long, curved bones called ribs. Below the lungs is a diaphragm which divides the trunk into an upper thorax and a lower abdomen. The ribs and the diaphragm play a major role in the breathing movements inspiration and expiration.
The coelomic fluid present inside the coelom contains four types of cells namely, Phagocytes, Mucocytes, Round Nucleated cells.