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Classification of Animals

Last Updated : 04 Mar, 2024
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The Classification of animals is based on the different characteristics of the living organism. The animal kingdom is also known as the ‘Kingdom Animalia’. The animal classification system divides organisms based on shared traits and evolutionary history. The presence and absence of the notochord form the basis of the classification of animals into two major groups: Chordates and Nonchordates.

Chordates include vertebrates like fish, amphibians, birds, and mammals, while Non-chordates include arthropods, mollusks, and annelids. It helps in understanding the evolutionary relationships and structural diversity within the animal kingdom. In this article, we will study animal classification in detail.

Animal Kingdom: Basis of Classification

Classification helps us to understand how all living organisms are related to each other. The system of animal classification was developed by Swedish botanist Carolus (Carl) Linnaeus in the 1700s. The animal classification taxonomy divides Kingdom Animalia into Phyla, Class, Order, Family, and Genus based on their characteristics. This Kingdom is divided into two major groups: Chordates and Non-chordates.

Also Read: Difference Between Chordates and Non-Chordates

Animals Classification Chart

Diagram below show the chart of classification of animlas in two major group: Vertebrates and invertebrates.

Classification of Animals

Classification of Animals

Animals are classified into two major groups on the basis of presence of presence and absence of the backbone into: Non-Vertebrates and Vertebrates. They are described in detail below:

Non- Vertebrates

Non-vertebrates or invertebrates are the animals that do not possess a vertebral column or backbone. It includes variety of animals such as porifera, arthropods, mollusca, annelids, cnidarians, etc. Different characteristics of invertebrates are given below.

  • They lack a backbone or vertebral column.
  • They show radial symmetry or bilateral symmetry depending on their evolution.
  • They are cylindrical, triploblastic, coelomate, or pseudocoelomate animals.
  • Respiration is either through gills, trachea or body surface.
  • Mode of reproduction can be sexual or asexual.
  • Fertilization is external, though internal fertilization also occurs in some species.
  • Open type of circulatory system is present.

The important characteristic features of the different phyla are described below.

Phylum – Porifera

The organisms belonging to this phyla are usually known as sponges. These sponges have the system of water transport system in their body. These are usually marine animals, which means most of them live in oceans and seas. These are multicellular organisms and have cellular levels. The skeleton of these organisms is made up of spicules. Reproduction in sponges is done asexually by the process of fragmentation and sexually by the process of Gametes formation. Fertilization in these organisms is internal. Examples: Euspongia and Spongilla.

Phylum – Coelenterata (Cnidaria)

These organisms are more symmetrical when compared to other organisms. These are mostly aquatic and free-swim animals that live in marines, seas, and other aquatic places. These organisms have Cnidoblasts on their tentacles and body. These Cnidoblasts are used in their defense mechanism and to capture the food. Cnidarians have mainly two body forms known as polyp and medusa. Polyp produces medusae using asexual reproduction and medusae produce polyp using sexual reproduction. Examples: Gorgonia, Meandrina, and Physalia.

Phylum – Ctenophora

Ctenophores are usually known by the names such as Sea walnuts. These are diploblastic organisms that live in marines and are radially symmetric. The organization in these organisms is of tissue-level organization. The process of digestion takes place both intracellularly and extracellularly. In Ctenophores reproduction takes place only by sexual reproduction. Fertilisation take place 
externally. Example: Pleurobrachia and Ctenoplana.

Phylum – Platyhelminthes

They have flattened body-like structures. So, they are called flatworms. These organisms are found in many living organisms including human beings. Parasitic worms have hooks and suckers on their body. Many of these flatworms absorb nutrients from their host’s body directly to survive. These organisms have special cells named flame cells which help in the process of excretion. Sexes are not separate in these worms. The process of fertilization occurs internally and development happens through several larva stages. Example: Taenia (commonly known as tapeworm) and Fasciola.

 Phylum – Aschelminthes

The shape of the body of Aschelminthes is circular. These organisms may be aquatic or terrestrial parasitic organisms that live in both plants and animals. These organisms choose either plants or other animals as their host and live. They have organs in their body. These organisms are bilaterally symmetrical in nature. Sexes are separate in these organisms as we can distinguish male and female in Aschelminthes. Usually, female are longer than male. The process of fertilization takes place internally and the development of the organism may be direct or indirect. Example: Ascaris (commonly known as roundworm) and Ancylostoma(Hookworm).

Phylum – Annelida

These organisms can live in both water and on land. They can live in both salt and fresh water. The organization of the body is organ level system. Their circular muscles and longitudinal muscles help in their locomotion. Their body surfaces consists of fragments. Nephridia help in excretion in these organisms. Reproduction in these organisms is sexual. Example: Nereis and Pheretima (common name is Earthworm).

Phylum – Arthropoda

The largest phylum among Animalia is Arthropoda. This phylum includes insects. Almost 66 percent of species on earth belong to the phylum of Arthropoda. The organisms in this phylum have organs in their body. These organisms are bilaterally symmetrical. In these kinds of organisms, excretion takes place through Malpighian tubes. Their bodies consist of the head, eyes, thorax, abdomen, etc. Respiration in Arthropods takes place through the lungs and gills. Fertilization is mostly internal and development happens either directly or indirectly. Examples: Apis(bee), Bombyx, Limulus, Locusta, and Anopheles.

Phylum – Mollusca

The second largest phylum after Arthropoda in the whole animal kingdom is the Mollusca phylum. The organisms that belong to this phylum are both aquatic and terrestrial animals. They can live in both fresh water and marine water. The body of these organisms is covered with a shell called a calcareous shell. With a muscular foot, visceral mass, and head, its body is unsegmented. The space between mantle and visceral mass is usually known as the mantle cavity. They have gills-like structures to breathe. These are mostly unisexual. Example: Octopus, Loligo, and pila

Phylum – Echinodermata

Mostly organisms belonging to the phylum Echinodermata are marine animals. They live in salt water. Fully grown echinoderms are radially symmetrical. But in the larva stage, they are bilaterally symmetrical. They possess a water vascular system for locomotion, the process of respiration, and capturing food. There are no specially defined excretory organs in these organisms. The nervous system and sense organs are poorly developed in echinoderms and the brain is absent. Sexes are mostly separate and the fertilization process is external. Example: Antedon, Cucumaria, and Ophiura

Phylum – Hemichordata

The phylum hemichordate was initially placed in the sub-phylum of Chordata. Now it is considered a separate phylum under non-chordates. These organisms are worm-like structures and mostly aquatic animals. They mostly live in marine water. Their body is in a cylindrical structure. Respiration in these creatures is done through gills that open into the pharynx. They have a dorsal heart. Example: Saccoglossus and Balanoglossus

Phylum – Chordata

Animals belonging to phylum Chordata are fundamentally characterised by the presence of a notochord, a dorsal hollow nerve cord and paired pharyngeal gill slits. These are bilaterally symmetrical, triploblastic, coelomate with organ-system level of organisation. They possess a post anal tail and a closed circulatory system.

Difference Between Chordata and Non-Chordata

The difference between Chordata and Non-Chordata are as follows:





Notochord present.

Notochord absent

Central Nervous System

Central nervous system is dorsal, hollow and single.

Central nervous system is ventral, solid and double.


Pharynx perforated by gill slits

Gill slits are absent.


Heart is ventral.

Heart is dorsal (if present).

Post-anal tail

A post-anal part (tail) is present.

Post-anal tail is absent.

Chordates are further classified into three subphyla:

  1. SubphylumUrochordata or Tunicata: The organisms in the subphylum Urochordata are marine organisms and we can find them from the surface to depths in the ocean. Their body is composed of a tunic which is formed by cellulose and their body is unsegmented. The circulatory system in their body is of circular type. Activities like free swimming develop in their tadpoles. They have a ventral heart which reverses the flow of blood. Example: Salpa, Pyrosoma, and Doliolum
  2. SubphylumCephalochordata: Cephalochordates are aquatic animals. We can find these animals mostly in marine water. They possess a notochord, pharyngeal slits, and tubular nerve chords. Respiration occurs through their body surface. The circulatory system in their body is closed type. Excretion in Cephalochordata is done through solenocytes. The process of fertilization is external. Example: Branchiostoma
  3. SubphylumVertebrata: The Subphylum Vertebrata is divided into many classes:
    • Amphibia
    • Reptilia
    • Aves
    • Mammalia
    • Pisces


Vertebrates are a subphylum of chordates that are characterized by the presence of a vertebral column or backbone. It encloses and protects the spinal cord. It includes animals such as fish, amphibians, reptiles, birds, and mammals. Different characteristics of vertebrates are given below.

  • They are characterized by the presence of a vertebral column or backbone. It encloses and protects the spinal cord.
  • They show bilateral symmetry.
  • Vertebrates have an internal skeleton made of bone or cartilage, providing structural support and protection for internal organs.
  • They are triploblastic, and coelomate with the organ-system level of organization.
  • The body have a closed circulatory system.
  • The notochord is present only in the larval tail, but in some, it is present throughout their life from head to tail region.

Also Read: Difference Between Vertebrates and Invertebrates

Conclusion – Animal Classification

Animal classification simplifies the study of biodiversity and helps in understanding evolutionary relationships. It divides the organisms based on their shared traits and evolutionary history into two major groups: Chordates and Nonchordates. This system of animal classification helps us understand the structural diversity within the animal kingdom and facilitates conservation efforts and species identification.

Also Read:

FAQs on Classification of Animal Kingdom

What is Animal Kingdom?

The animal kingdom, or Animalia, is a major biological kingdom. It consists of multicellular, eukaryotic organisms charactertised by heterotrophy and mobility. They have diverse form, features and life forms.

What are the Two Main Groups of Animals?

The two main groups of animals are vertebrates and non-vertebrates. They are grouped on the basis of presence and absence of the vertebral column.

What are the Major Classification of the Animal Kingdom?

The major classification of the animal kingdom are Phylum Porifera, Phylum Coelenterata (Cnidaria), Phylum Ctenophora, Phylum Platyhelminthes, Phylum Aschelminthes, Phylum Annelida, Phylum Arthropoda, Phylum Mollusca, Phylum Echinodermata, Phylum Hemichordata and Phylum Chordata.

What are the 7 Classifications of Animals?

The 7 classification of animals are kingdom, phylum or division, class, order, family, genus, and species. The animal kingdom is the largest of all five kingdoms.

Who is the Father of Taxonomy?

Father of taxonomy is Carl Linnaeus, also known as Carl von Linné or Carolus Linnaeus.

State any 4 Benefits of Animal Classification?

Animal classification simplifies the study of organisms, helps in understanding evolutionary relationships, provides a basis for conservation efforts, and helps in the identification of species for scientific research purposes.

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