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Kingdom Animalia – Definition, Classification, Characteristics

Last Updated : 25 Jul, 2022
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There is a wide number of creatures that are near and particular to one another at various points. In this manner, people from a particular gathering of creatures share a particular brand name. This is the part that portrays the gathering.

Swedish botanist Carolus Linnaeus (1707-1778), found the Modern System of Scientific Classification. The structures most specialists use arrange each living thing into seven gatherings or taxons. These characterizations in the progressive system are from the top most and generally far-reaching to the least and more specific are:

Kingdom – Kingdom is the most amazing fundamental division where all articles are set. The Animal Kingdom includes all creatures on the planet.
Phylum – We can isolate every realm into more modest developments called phyla. For instance, Chordates are a phylum with people having the notochord.
Class – We can isolate chordates into classes. For instance Mammalia, Birds, Reptilia, and Amphibians.
Family – We can isolate classes into families. Families contain more than one variety.
Genus – Families are sub-parceled into genera. Creatures that have similar sort are generally something very similar.
Species – Species are the most critical and contain just a single sort of creature.

Animals have been categorized into two primary categories in the animal kingdom based on the presence or absence of a backbone or spinal column.

  • Vertebrates
  • Invertebrates


Vertebrates are the animal kingdom’s most advanced species. Members have an internal skeleton system with a backbone that is well defined. The spinal cord connects the nerve tissues in humans as it passes along the body between the caudal and cranial regions. In comparison to invertebrates, vertebrates have more sophisticated and specialized organ systems. Organ systems, such as the respiratory system, are extremely complicated, having numerous functions. Even the sensory organs have improved, allowing vertebrates to adapt to their surroundings. The total number of vertebrates on the globe is estimated to be between 57,000 and 58,000. All chordates, such as mammals, birds, fish, reptiles, and amphibians, are examples of vertebrates. The members of the vertebrates have bilaterally symmetrical bodies.


Animals without a backbone are known as invertebrates. They are abundantly distributed, found anywhere, from the hottest deserts to the deepest seabeds, as well as the deepest caves and highest mountains.

Invertebrates are animals that do not have a skeletal system, as previously stated. As a result, the majority of them lack a hard body structure and thus are unable to grow very large. Blood flows in an open cavity in most invertebrates’ circulatory systems. A basic respiratory system is found in most invertebrates, with gills and a trachea being the most prevalent. Most invertebrates have an exterior skeleton to protect their soft, inner body since they lack an internal skeleton. Chitin, a glucose derivative, is commonly used to make this substance. Invertebrates account for more than 97 percent of all animal species on the planet. More than 2 million species of invertebrates have been discovered, with new ones being discovered virtually every day.

Annelids, arthropods, bivalves, coelenterates, echinoderms, squid, sponges, snails, and octopuses are only a few examples. Some invertebrates have qualities and characteristics that are significantly superior to those of vertebrates.

Subphylum Vertebrate

The Phylum Chordata is divided into vertebrates and invertebrates. The subphylum Vertebrata or Craniata includes all vertebrates and craniate. Zoologists are more prone to create more subphyla than Vertebrata as a result of the new information. Other than Vertebrata, Nelson (1994) mentions the subphyla Conodontophorida and Craniate in his concept. In most modern literature, the terms Vertebrata or Craniata are used interchangeably.

The Animalia is divided into phyla as follows

Phylum Porifera

Porifera refers to organisms that have holes in them. A sponge is a common name for them. Porifera has the following characteristics:

  • Multicellular organisms with a rigid exterior skeleton are not mobile.
  • Have a body that is permeable.
  • The pores on our bodies form a canal system that aids in medication circulation.
  • Their bodies lack a normal head and tail, as well as well-developed organs and organ systems.
  • Include habitat from the sea.
  • Spongilla and Sycon are examples of the Porifera phylum.

Phylum Coelenterate (Cnidaria)

The name “Coelenterate” comes from the Greek word “kilos,” which means “hollow-bellied.” They have the following characteristics:

  • Have a bodily cavity that is hollow.
  • The body is divided into two parts.
  • All aquatic animals are included.
  • Inner and exterior linings are two layers of cells that make up the human body.
  • They can be found alone (Sea anemone) or in colonies (Sea anemone) (corals).
  • Hydra and jellyfish are examples of the phylum Coelenterate.

Phylum Platyhelminthes

Flatworms are the popular name for Platyhelminthes. They have the following characteristics:

  • The body is flattened dorsoventrally.
  • The body structure is complex and differentiated.
  • They are triploblastic, meaning that the tissue is made up of three distinct cell layers.
  • There is no true interior cavity or coelom.
  • Have symmetry on both sides.
  • Planaria are either free-living or parasitic (liver flukes).
  • Tapeworm and Planaria are examples of Platyhelminthes phylum.

Phylum Nematoda

Nematodes, sometimes known as roundworms, belong to the Phylum Nematoda. They have the following characteristics:

  • The body of a nematode is cylindrical.
  • Triploblastic and bilaterally symmetrical.
  • Have a fake bodily cavity and pseudo color.
  • Elephantiasis and ascariasis are parasitic disorders caused by this parasite.
  • Ascaris and Wuchereria are examples of Nematoda phylum.

Phylum Annelida

Annelids are sometimes known as segmented worms or ringed worms. They possess the following characteristics:

  • The body is segmented and cylindrical.
  • The body is divided into two parts: the head and the tail.
  • Triploblastic and bilaterally symmetrical.
  • Have a real cavity in your body.
  • Marine, freshwater, and terrestrial habitats are all present.
  • Earthworms and Leech are examples of the Annelida phylum.

Phylum Arthropoda

  • The term “arthropod” refers to a creature with jointed legs. The current phylum includes animals with jointed appendages. Within the Animalia, this is the most important phylum. 
  • They are symmetrical on both sides.
  • Have segmented bodies, jointed appendages, and an exoskeleton.
  • Have organs and organ systems that are well-differentiated.
  • Have an open cardiovascular system with no distinguishable blood arteries.
  • Butterflies, spiders, and mosquitoes are just a few examples.

Phylum Mollusca

The Mollusca phylum is made up of a large number of species. The following features are included:

  • Triploblastic and bilaterally symmetrical.
  • Body with fewer segments.
  • Organ and organ system development.
  • An open circulatory system is usually present.
  • There are limbs present.
  • Snails and octopuses are examples of the Mollusca phylum.

Phylum Echinodermata

Echinodermata is derived from the Greek terms echinos, which means hedgehog, and derma, which means skin. Echinoderms are animals with spiky skin.

  • Triploblastic symmetry and radial symmetry
  • Have a true sense of coelom.
  • Have a skeleton made of calcium carbonate.
  • Marine animals that live in the open ocean.
  • Sea urchins and starfish are examples of the phylum Echinodermata.

Phylum Hemichordate

The following are the characteristics of the phylum Hemichordate:

  • The body is separated into a proboscis, which is soft and fragile
  • The epidermis is made up of only one layer.
  • Includes worm-like aquatic creatures with the organ-system organization.
  • They have a circulatory system that is open.
  • Because they are marine, they breathe through their gills.
  • The sexes are separated, and conception takes place outside the body.
  • Development is a direct process.

Phylum Chordata

The following are the properties of Chordates:

  • The body is bilaterally symmetrical, organ-system organized, and triploblastic.
  • They have a nerve cord and a notochord.
  • The circulatory system is one that is closed.
  • Chordata is often subdivided into the following subphyla:
    • Urochordata
    • Cephalochordate
    • Vertebrata

There are a couple of significant qualities that are customary to various life forms. In this manner, we genuinely must be familiar with the different parts. These parts incorporate body evenness, nature of coelom, the game plan of cells, notochord, examples of circulatory, stomach related, and conceptive systems, division, and a course of action of cells in microorganism layers. Presently we will check out these parts in subtleties.

Levels of Organization

Each organic entity of the Animalia realm is multicellular. Notwithstanding, they don’t show a similar illustration of cell association. The instances of cell association found in creatures are:

Cell-Level of Organization – In such creatures, the cells are coordinated as free cell knots. We can see this kind of cell association in wipes. Outline: Sponges.

Tissue Level of Organization – Animal cells show the division of activities in the midst of themselves. Cells completing a similar limit are coordinated as tissues. Representation: Coelenterates.

Organ Level of Organization – We bunch the creature tissues doing comparable limits into shape organs. Each organ is explicit for a specific limit. Representation: Platyhelminthes.

Organ structure Level of Organization – In creatures where organs have connected with shape useful systems where each structure is connected with a specific physiological limit, show organ system level of association. Models incorporate Mollusca, Chordates Annelids, and so on.

Body Symmetry

We can arrange creatures based on the balance of their body. The strategy of body parts around a mainline or point chooses the evenness. Deviated: We can’t segment these creatures into two comparable parts alongside any plane going through their point of convergence. Model: Sponges. Outspread Symmetry – Animals will generally show twisting balance. This implies that any plane going through the central turn of the body parcels the creature into two vague parts. Model: Ctenophores and Echinoderms. Reciprocal Symmetry – Animals, where the body can be parceled into undefined right and left parts, are respectively balanced. Model: Annelids, Arthropods, and so forth.
Notochord Chordates are creatures with a notochord. Then again, non-chordates are the creatures without a notochord. Model: Porifera to Echinoderms.

Conceptual Questions

Question 1: What are the different types of animals?


The existence or lack of a backbone is one of the most well-known and basic means of classifying animals. There are two types of animals that fall under this classification: vertebrates and invertebrates.

Question 2: Describe the characteristics of invertebrates in a few words.


The lack of a spinal cord is one of the most distinguishing features. This means that members of this class lack an internal skeleton that is hard and bony. The exoskeleton, a hard, external structure that offers structural strength and protection from predators and the environment, is found in some members (e.g., crabs, lobsters, and ammonites.) The majority of the members are motile, but others, such as the sea sponge, are not.

Question 3: Describe the characteristics of vertebrates in a few words.


In comparison to invertebrates, vertebrates are more complicated organisms. Vertebrates have a backbone and an internal skeleton, which distinguishes them from other animals. In some species, such as sharks, the bones are replaced with cartilage. Vertebrates also reproduce sexually, which is another distinguishing feature.

Question 4: What role do pneumatic bones and air sacs play in the anatomy of waves?


Pneumatic bones have a hollow interior filled with air, which aids in flight. The air reservoirs are the air sacs. They also serve as cooling devices and control body temperature.

Question 5:  What do you mean when you say metagenesis? Give a specific example.


Metagenesis is the process through which an asexually reproducing generation of plants and animals is followed by a sexually reproducing generation. Coelenterates, for example.

Question 6:  What role do feathers play in birds?


The feathers aid in the regulation of body temperature. They provide wings of an airfoil shape to aid in flight. In both sexes, they serve as secondary sex characteristics. Mates are attracted to the color and markings.

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