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Monday, December 26, 2011

Criteria in the Natural Classification of Animals

I mentioned how to classify plants with using natural classification system as flowering plants and non-flowering plants. So now I'm going to classify Animals like that.

Around one million species of animals have been identified by now. More animals are still being discovered and identified by using various investigations. All these animals have a common relationship. In a natural classification the phylum and genetic relationship is well displayed.

The classification of animals has been developed better in the 10th edition of "System Nature" written by Linnaeus in 1758. This is the classification used at present.

Vertebrates

The vertebrates are considered to be a key group of animals in the animal kingdom. Some of the main characteristics of vertebrates are:
  • The presence of a hollow, tubular nerve cord.
  • The nerve cord forming a brain at the anterior end.
  • Availability of bony skull covering the brain.
  • Availability of a vertebral column covering the rest of the nerve cord.
  • Presence of a post anal tail.
  • Most advanced mentally developed group of animals.
animals of group vertebrates
Animals of Group Vertebrates
As all animals with a vertebral column(backbone) are vertebrates, all other multicellular animals without a backbone are know as invertebrates.

The vertebrates are classified under 5 categories.
  1. Fish - Pisces
  2. Amphibians - Amphibia
  3. Reptiles - Reptilia
  4. Birds - Aves
  5. Mammals - Mammalia

1. Fish - Pisces

  • They are aquatic animals.
  • Fins are available for swimming.
  • Live in fresh water or brackish or salt water.
  • The gills are the main respiratory organs.
  • Their mode of movement in water is swimming. They posses a streamlined body. 
  • There is evidence to show that life on earth(land) evolved from the fish.
  • Oxygen required for breathing is obtained mostly from the water and at times from the atmosphere.

2. Amphibians - Amphibia

  • They are laying eggs.
  • Most of them have 4 legs.
  • They have the ability to swim in water and either crawl or hop on land.
  • They live in both aquatic and land environments. Webbed feet are seen.
Examples: Frog, Toad

Note:The tadpole stage of a frog in its life cycle is very similar to a fish. It has external gills. This proves Haeckel's theory on evolution of life that any animal displays its ancestral history.

3. Reptiles - Reptilia

  • Live on land.
  • Born out of eggs.
  • They are animals that crawl.
  • Most of them posses 4 limbs.
  • Reptiles who do not have limbs are known as snakes.
Examples: Lizards, Tortoises,  Snakes.

4. Birds - Aves

  • Bones are hollow.
  • Warm blooded animals.
  • The mode of movement is flying.
  • Front limbs are adapted as wings.
  • Possess a beak. No teeth in the mouth.
Examples: Eagle, Sparrow, Pigeon.

5. Mammals - Mammalia

  • Warm blooded animals.
  • Most developed group of vertebates.
  • Body divided into head, neck and trunk.
  • Live in all three - air, land and aquatic environments.
  • The external ears(pinnae), nose and the eyes in the head can be easily identified.
  • Possess well - developed fore limbs. They are used either to walk, swim or fly according to the environment they live in.
  • Feed on milk.
Examples: Chimpanzee, Elephant.

Now I think you are familiar with vertebrates. Now you might be searching for Invertebrates, But It's not here. It'll be my next article. So come again..! Until then Good Luck

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