There are more than 2.5 million species of animals in world. It is very difficult to study each and every specie without classify into a proper manner. Even some species look same. Hence, it is very necessary to classify animals. Classification helps us understand the relationship among different group of species.
Based on nature
On the basis of nature of animals, they are classified into two types - wild animals and domestic animals. Animals that can not be reared are called as wild animals. Tigers, lions, bears, etc are wild animals. Animals that can be reared are called as domestic animals. Dogs, cats, sheeps, goats, etc are domestic animals.
Based on number of cells
On the basis of presence of number of cells, animals are classified into unicellular animals and multi-cellular animals. Animals that made up of only one cell are called as unicellular animals. Amoeba, paramecium, etc. are some of the examples of unicellular animals. Animals that made up of more than one cell are called as multi-cellular animals. The bodies of animals like the ant, mouse, elephant, fish, etc. are made up of many cells.
Based on habitat
On the basis of place where animals live (habitat), they are classified into terrestrial, aquatic and amphibious animals. Animals that live on land are called as terrestrial animals. Dog, fox, lion, elephant, etc are terrestrial animals. Animals that entirely live in water are known as aquatic animals. Fish, jellyfish, octopus, etc are some of the aquatic animals. Some animals like frog, tortoise, crocodile, etc can survive in land as well as water. They are known as amphibious animals.
Based on presence of vertebral column
• Depending on whether an animal has or does not have a vertebral column, animals are classified into vertebrate animals and invertebrate animals. If we draw a finger down the middle of our back, we shall feel a chain of bones. Each of these bones is called a vertebra and this chain is called the vertebral column.
• Animals that have a vertebral column are called as vertebrate animals. Examples of vertebrate animals - fish, frogs, lizards, snakes, chameleons, sparrows, crows, rabbits, elephants, monkeys etc. About 2% of total animal species are vertebrates. Animals that do not have a vertebral column are known as invertebrate animals. Animals like amoeba, worms, earthworms, snails, crabs, butterflies, etc do not have a vertebral column. About 98% of total animal species are invertebrates.
• Vertebrates can be further classified based on the type of their body covering. Generally, the skin protects an animal’s body. Vertebrates have an additional covering for protection. It may be made of scales, hair or feathers. Thus, vertebrates may be classified into three groups as animals with scales, with hair and with feathers. Animals like fish, snakes, lizards, chameleons, tortoises have scales on their bodies. Dogs, rats, monkeys, bears, etc bears have bodies covered with hair. Crows, eagles, kites, parrots, peacocks have feathers. Feathers help them for flying.
Based on mode of reproduction
On the basis of mode of reproduction, animals are also classified into oviparous animals and viviparous animals. Animals that are hatched out of eggs are known as oviparous animals. A sparrow, snake, etc lays eggs and hatches them. In a few days, the sparrow’s and snake’s young ones break the eggs and come out. Animals that give birth to young ones are called as viviparous animals. The growth of a bitch’s young one first takes place inside the bitch’s body. When this growth is complete, the bitch gives birth to puppies.
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