Animal is the term that applies in general to all the creatures that can move. The biological world is made up of plants and animals. Animals can range from very simple forms to very complex ones. They are categorized into vertebrates and invertebrates, based on the presence or absence of a spinal cord. Roughly, animals can be classified as follows:
Fish: Fishes are found in water. They inhale through fins and through their skin. Fish eat insects or plants from the water. Often larger fish eat other fishes. Fishes lay eggs as a part of the reproduction process. They have streamlined bodies to adapt to movement in water.
Insects: Insects are very small in size, multiplying very fast. A head, abdomen and thorax with feelers, wings and limbs are the common feature; however, some are extremely beautiful like the butterflies. Insects help in pollination. They lay eggs to continue the reproduction cycle.
Birds: Birds are the winged creatures, most of them with the ability to fly. Some like the penguins cannot fly. They have a feathered body and feet with claws for holding the branches. Wading birds have webbed feet. They have beaks to prey on insects, seeds and often can also be scavengers. Birds too lay eggs.
Amphibians: Amphibians can live on land as well as water. Frogs, turtles can breathe through lugs and can take in also through their skin.
Reptiles: Snakes, lizards and crocodiles are examples of reptiles that are comfortable in land and water.
Mammals: All animals that do not lay eggs but have babies and suckle them are mammals. Whales and dolphins, even though marine animals, are mammals. Man too is a mammal. Most of the mammals have four legs. Apes, Lions and the common animals are usually mammals.
Animals are an essential part of life. To humans some animals are useful but to nature each of them has a part to play. There is delicate balance maintained by the food chain and each one has a significant role, probably except man.