Give outline representation of animal kingdom
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Classification of Animal Kingdom: Outline, Levels and Divisions
OUTLINE OF ANIMAL CLASSIFICATION
Body structures or body plans form an important base for the characterization and classification of animals. Body plan is also referred to as bauplan in the German language.
Body plan 1: Number of primary germ layers in the embryo
Based on the number of primary germ layers in the embryo, the animals can be divided into two types, namely diploblastic and triploblastic.
Animals form layers of cells during their development from a single-celled zygote stage to multicellular adult. The embryo of the diploblastic animals has two cell layers, an outer ectoderm and an inner endoderm.
On the other hand the embryo of the triploblastic animals as an additional third layer called as the mesoderm between the ectoderm and the endoderm. This existence of the three layers differentiated protostomes and deuterostomes from simple animals that have evolved earlier.
Body plan 2: Division of labor
Based on the division of labor, animals are divided into three types namely, cellular grade of organization, tissue grade of organization, organ grade of organization.
When the specific body functions are performed by cells it is called as cellular grade of organization. When the specific body functions are performed by tissues it is called as tissue grade of organization. Finally when the specific functions are performed by the organs or organ systems it is called as organ grade or organ-system grade of organization.
Body plan 3: Body cavities
Animals can be grouped into three main categories based on the types of body cavity they have namely acoelomates, pseudocoelomates and coelomates.
Acoelomates are the animals which lack the body cavity or coelom. The space between the gut and body wall is filled by mesenchyme tissue. Example of acoelomates is phylum Platyhelminthes. On the other hand pseudocoelomates are animals with pseudocoelom which is not lined by peritoneal layers. Example of pseudocoelomates is phylum Nemathelminthes. The pseudocoelom is a liquid filled space in which organs are suspended. Finally coelomates are the animals which develop a coelom within the mesoderm. The coelom is lined by peritoneum. Example of coelomates is all the animals from phylum Annelida to Chordata.
Body plan 4: Symmetry
Based on the symmetry, animals can be divided into two types namely, bilateral symmetry and radial symmetry.
Bilateral symmetry is always associated with cephalization. Cephalization is the presence of head bearing sensory organs and a central nervous tissue at the anterior end of the animals. Both the bilateral symmetry and cephalization are common in the animals that move freely. These are the animals that can only be cut in one plane to create a single mirror image. They have top (dorsal), bottom (ventral), head (anterior), tail (posterior), right, and left sides.
On the other hand radial symmetry is very much primitive to bilateral symmetry. These are the animals that can be divided multiple times through a central axis creating multiple mirror images. They have a top and a bottom but no left nor right, no head nor tail.
Body plan 5: Fate of blastopore
Based on the fate of blastopore, animals can be divided into two types namely, protostomes and Deuterostomes.
Protostomes in Greek means mouth first. They are the organisms in which the blastopore develops into mouth. Hence in these animals the mouth is formed first. Cleavages in protostomes are spiral and determinate type. In spiral cleavage, the cleavage planes are oblique to the polar axis of the zygote. In determinate cleavage, the fate of blastomeres is fixed early in the development.
On the other hand deuterostomes in Greek means mouth second. They are the organisms in which the blastopore develops into anus and the mouth is formed later. Cleavages in deuterostomes are radial and determinate. In radial cleavage, cleavage plans are at right angles to the polar axis of the zygote. In indeterminate cleavage, the fate of blastomeres is fixed later in the development.
Body plan 6: Gut
Based on the gut or digestive tract, the animals can be divided into two types namely, extracellular and intracellular.
The digestive tract enables the animals to digest food outside cells. This digestion is also called as extracellular digestion. In some animals which do not have a digestive tract, the food items are brought into the cell for digestion. This type of digestion inside the cell is termed as intracellular digestion.
Body plan 7: Circulation of blood
Based on the circulation of blood the animals can be divided into two types. Namely open type of circulation and closed types of circulation.
In open type of circulation the blood circulated in the open cavities called sinuses. On the other hand, the blood circulated only in the closed blood vessels in closed type of circulation.