Animal Kingdom


Kingdom Animalia is one of the unique classification with a variety of species based on different criteria. According to Whittaker, the Animalia kingdom encompasses various multicellular eukaryotic animals. It is one of the major kingdoms among the top-5 kingdom scheme of classification. Based on the Patterns of circulation, digestive and reproduction, body symmetry, Nature of coelom, cellular arrangement, Notochord, and pattern of segmentation, Kingdom Animalia is classified as follows. Based on the organ systems digestive, circulatory, and reproductive function.

Table Of Contents

1. Introduction

2. Patterns of Organ System

   2.1 On the basis of body symmetry

   2.2 On the basis of body Wall of animals

   2.3 On the basis of the nature of Coelom

   2.4 On the basis of segmentation

   2.5 On the basis of the presence or absence of notochord

3. Levels of Organization of animals

4. System of Classification of Animal Kingdom

Patterns of Organ System

Different animals have different frameworks of organs.

  1. Digestive System – There are two forms of digestive framework Complete and Incomplete Digestive Framework. In an incomplete Digestive framework, the digestive system has only one opening to the outside of the body. The opening is a solitary opening that acts as both mouth and rear-end. One of the example is Platyhelminthes. In a Complete Digestive Framework, there are 2 different openings to the outside of the body, a mouth and a rear-end. F0r example, Arthropods, and Chordates.

  2. Circulatory System can be closed type and open type. In an open circulatory framework, the blood is pumped out of the heart resulting in a gush of blood against every cell. For instance, arthropods and molluscs. On the other hand, a closed circulatory framework is the one in which the blood is gradual and moves through different vessels - the arteries, veins, and capillaries. Vertebrates belong to this group.


 On the basis of body symmetry

Based on the symmetry, the animals can be categorized as radial and asymmetrical ones. Asymmetrical types of animals are those that can't be partitioned into 2 equal parts (bilateral asymmetry) along any plane going through the focal point of the organism. For example, Sponges. Radial Symmetry is when the animals tend to exhibit spiral symmetry on any plane where the body partitions give rise to2 indistinguishable parts. Example, Ctenophores, and coelenterates. On the other side, bilateral Symmetry is a condition where an animal’s body can be partitioned into indistinguishable right and left parts and they are bilaterally symmetrical. For example, Annelids, Arthropods.


On the basis of body Wall of animals

Based on this, animals are organized into diploblastic animals such as Coelenterates where there are  2 layers of the body wall and triploblastic animals have 3 body layers I,e germinal layers, the external ectoderm, inward endoderm, and the third germinal layer mesoderm. For example, Platyhelminthes to Chordates.


On the basis of the nature of Coelom

Coelom is the body cavity lined by the mesodermal cells. Animals can be classified based on the presence or absence of a body cavity in between the gut wall 3 main class of animals base on the nature of coelom are Acoelomates, Pseudocoelomates or Coelomates. Acoelomates are the invertebrates that lack a coelom. For example, flatworms and nemerteans. Pseudocoelomates are those animals where the body cavity is not formed by the actual pattern of mesoderm cells, instead, the mesoderm is scattered between the endoderm and the ectoderms. For example, Aschelminthes. Coelomates have the body cavity that is lined by the mesoderm. For example, Arthropods and Chordates. 


On the basis of segmentation

 Based on the segmentation, animals are called metameric, where the body is segmented from inside to outside, with serial redundancy of few organs. For example, Earthworm.  


On the basis of presence or absence of notochor

 Few animals can be chordates (the animals which have Notochord) and few are Non- Chordates (Animals that lack notochord) for example, Porifera to Echinoderms.  


Levels of Organization of animals

Although eukaryotes share a common basis of the organization of the body (cell, tissue, organ), they differ because some of them belong solely to cellular and few are tissue-level classes and many advanced animals have many systems.  The examples of cellular organization are as under:

In organisms such as Sponges, the cells are organized as free cell lumps. When animal cells show division of exercises amid themselves this is known as tissue level organization as seen on the coelenterates. In an organ level of organization, animals are classified based on similar tissues are grouped to form the organs and they perform similar functions, hence every organ has a particular capacity. For example all Platyhelminthes. When every organ framework is related to a particular physiological capacity then it is called as Organ framework Level of Organization. For example, Mollusks and Annelids.

Levels of organisation


System of Classification of Animal Kingdom

Swedish botanist Carolus Linnaeus (1707-1778) has introduced the modern System of Scientific Classification. He considered the animal`s kingdom, phylum, class, family, genus and species to classify as under.

  1. Kingdom – Kingdom is the prime level division in which, a kingdom includes all of the members. For instance, the animal kingdom involves all the animals in the world.

  2. Phylum is the next division where each kingdom is further divided into smaller subdivisions called phyla, for instance, chordates are a phylum with individuals having the notochord.

  3. When chordates are further separated, they give rise to many classes, For Example Birds, Reptilian, Mammalians, and Amphibians form this class.

  4. When classes are further categorized, they give rise to the family – a family has more than one genus.

  5. If the families are sub-partitioned, they result in Genus or genera. Animals that have the same genus are fundamentally the same as and most likely developed from the same common predecessor.

  6. Species – Species is the most crucial and contains only one kind of animal.  ​​​​​​




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