Animals are multicellular, living organisms in the Kingdom Animalia. With few exceptions, all animals breathe oxygen, eat organic matter, can move, reproduce sexually, and secrete body waste. Although all of these traits are derived from animals’ ancestors, which are mostly amphibians and fishes, some have evolved into more modern forms such as cows, sheep, deer, and pigs. In this article, we will briefly discuss some of the major groups of animals that we care for.


First, there are laboratory animals such as rats, mice, guinea pigs, chickens, and other birds. These animals are usually used in a number of types of animal experiments. For instance, guinea pigs are used to test the effects of stress on the neurological system, and they are also used in tests of the effects of certain cancer drugs. Other animals used in animal experiments include dogs, bees, and other insects. Other animals that are sometimes used are amphibians and reptiles.

In order for animals to belong to the kingdom Animalia, they must possess a centralized nervous system along with the other characteristics that define animals. All vertebrates including humans have nervous systems. The nerves pass signals between brain and body through the spinal cord and the limbs. Body movements make sure that messages are transmitted from one part of an animal to another. All animal bodies are characterized by coordinated pattern of muscles. The nerves that make up the spinal cord pass messages from the brain to the various animal organs through these muscles.

All animal body is composed of multicellular organisms called somatic cells. In contrast to the cells found in our bodies, in the animal kingdom animals have no cell wall. This is a very important point because the cell wall is the only component that prevents the spread of infections and is capable of protecting the organism from external agents. Cell wall enables the animal to secrete hormones, enzymes, vitamins and other nutrients necessary for growth, development and metabolism. The major division in animal cells is protein-based cells such as red blood cells and muscles. There are also chemical elements in animal cells, which form complex assemblies called peptides.

Insectivores and plantivores have their own unique attributes, whereas carnivores have a specialized anatomy for preventing intrusions into their appetites. The diet of most mammals consists of vegetation or plant extracts while aquatic animals mostly feed on fish and other aquatic life. Most salamanders are amphibians. A few species of salamanders are well-known as the only true carnivores.

Many animals have evolved from more ancient forms of animal body plans like reptile ancestors. Eutherians and placerivores are the descendants of amphibians. amphibians are known to have lived for half of Earth’s history. Evidence of animal tissue is found in the fossil record. The fossil record shows us that dinosaurs disappeared about 65 million years ago.

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