Kingdom Animalae:

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Characteristic features of kingdom Animalia:

These are multicellular organisms and made up of eukaryotic cells. The cells do not contain cell wall, but contain only cell membrane. They are heterotrophic, i.e. they do not perform photosynthesis and depend on others for food. They have the power of locomotion, i.e. they are mostly motile. They show increased sensitivity through the nervous system.

Basis of classification of animals:

There are many features used for distinguishing broad categories of animals. These features include organization, symmetry, body cavity, number of embryonic cell layers and presence or absence of notochord.

Organization: Animals are multicellular, but their body cells may or may not be organized into tissues and organ systems. Example is animals such as sponges are aggregate of cells. They are at a cellular level of organization. Human beings have organs and organ systems for performing body functions and are at the organ-system level of organization.

Symmetry: It means dividing the body into equal and identical parts. Sponges are symmetrical. Cnidaria are radially symmetrical and all other animals are bilaterally symmetrical.

Image showing symmetry.

Image Showing Symmetry.

Image showing symmetry.

Body cavity: Body cavity or coelom is a cavity between the body wall and the food canal. It is absent in Acoelomates and present in Eucoelomates. The body cavity of roundworms is not true and is known as pseudocoelom.

Embryonic layers: There are three layers of cells; ectoderm (Outer layer), mesoderm (middle layer) and endoderm (inner layer) in the embryo which give rise to parts of the body of animals. Sponges and Cnidaria do not have mesoderm in their embryos and are called diploblastic. Other animals have three layers of cells and are called triploblastic.

Notochord: The notochord is a stiff rod running along the body, close to the dorsal surface. The notochord helps to provide support to the animal. All chordates possess a notochord at some stage of their environment. The notochord is absent in invertebrate animals, also termed as non-chordates.

Image showing basic classifcation of animalia.

Image Showing Basic Classification of Animalia.

Image showing basic classifcation of animalia.