Classification of Animal Kingdom:

The science of classifying organisms is called taxonomy.  Taxonomy is a means of arranging living things into orderly groups. These groups are mostly distinguished by structure and reflect evolutionary relationships. There are seven level of classification such as:

1)      Phylum

2)      Class

3)      Order

4)      Family

5)      Genus

6)      Species

Highest classification level is kingdom; it incorporates organisms that share only a few important features. To classify this group we divide them into two groups:

1)      Non- chordates

2)      Chordates

Word Origin:

In 1926, from latin (in) not + (vertebra) joint. Invertebrates as biological classification were coined in 1805 by French naturalist Georges Loopole, Chretien Frederic Dagobert, Baron Cavien.



Non chordates are animals without notochord. They are the most abundant diversified of all animals living or extinct.

Characteristics of Non chordates:

Ø  Notochord absent.

Ø  Pharyngeal gill slits are absent. It means pharynx is not perforated by gill slits or paired openings.

Ø  Post anal tail absent.

Ø  Nerve cord if present is double, ventral and solid.

Ø  Heart is dorsal in position if present.

Ø  Hepatic portal system is absent.


1.       Protozoa

2.       Porifera

3.       Coelentrata

4.       Platyhelminthes

5.       Aschelminthes

6.       Annelida

7.       Arthropoda

8.       Mollusca

9.       Eied chinodermata



Ø  They are unicellular, microscopic organisms.

Ø  They are free living, symbiotic or parasitic in nature. (Free living are mostly aquatic or terrestrial)

Ø  Locomotion is through pseudopodia, cilia and flagella.

Ø  Locomotary organ is the basis of classification in protozoans.

Ø  Ingestion of food by phagocytosis or pinocytosis.

Ø  Asexual reproduction by binary fission.

Ø  Sexual reproduction by conjugation.

Ø  Eg: Amoeba, Paramecium, Plasmodium, Euglena


Ø  Primitive muticellular exclusively marine animals, few in fresh water.

Ø  They are solitary and colonial.

Ø  They are sessile and fixed.

Ø  They have cellular level of organization.

Ø  Simplest animals having pores called ostia through which water enters into the body or ingestion occurs and osculum through which water emits out of the body of organisms or egestion occur. This is known as canal system, it’s a basis of classification in porifera.

Ø  Asexual reproduction occurs by budding.

Ø  Also possesses a great power of regeneration.

Ø  Eg: Sycon, Spongilla, Euplectella.


Ø  Aquatic, mostly marine animals.

Ø  They are sessile or free swimming animals.

Ø  They are solitary or colonial.

Ø  Radially symmetrical, body wall is diploblastic  with tissue level of organization.

Ø  Mouth is surrounded by central gastovascular activity having cnidocytes (stinging cells) for capturing of food and offence and defence.

Ø  Coelentrates are carnivores with intracellular and extracellular digestion.

Ø  Coelentrates are characterized by alteration of generation, where polyp (cylindrical) is altered by medusa (umbrella) stage.

Ø  Asexual reproduction handled by budding and they have great power of regeneration.

Ø  Eg: Hydra, Sea anemone, Physalia, Aurelia.


Ø  Platyhelminthes possess dorsoventrally flattened thin body.

Ø  They are bilaterally symmetrical and triploblastic animals.

Ø  Platyhelminthes are acoelomate animals with organ level of organization.

Ø  Platyhelminthes are also known as flatworms.

Ø  They are mostly endoparasites found in the digestive system of animals including humans also.

Ø  Parasitic members possess hooks and suckers, some of them use the surface of their body to absorb nutrients directly from the host.

Ø  Eg: Taenia solium, Fasciola hepatica

Aschelminthes or Nematodes:

Ø  They are also known as roundworms because they have circular body when seen in cross section.

Ø  They are long, slender and cylindrical worms.

Ø  Aschelminthes are aquatic or terrestrial free living or parasitic on plants and animals.

Ø  They are bilaterally symmetrical, triploblastic body covered by a thick cuticle.

Ø   Pseudocoelomate animals with organ level of body organization.

Ø  They are unisexual organisms.

Ø  Eg: Ascaris lumbricoides, Wucheria bancrafti.


Ø  They are free living organisms.

Ø  Annelids are cylindrical or elongated organisms.

Ø  Annelids are characterized by metameric segmentation.

Ø  Their locomotary organs are setae, parapodia or suckers.

Ø  Hermaphrodites with separate sexes.

Ø  Eg: Earthworms, Leech, Neries.


Ø  Largest animal group among all invertebrtaes.

Ø  They are found in all habitats.

Ø  Triploblastic, coelomate, bilaterally symmetrical.

Ø  They have segmented body with heads having paired jointed appendages for locomotion.

Ø  Chitinous exoskeleton covering the body.

Ø  Bisexual reproduction or sexes are separate.

Ø  Eg: Crab, Spider, Millipede, Cockroach


Ø  They are aquatic or terrestrial.

Ø  Molluscans have triploblastic and coelomate body.

Ø  They have unsegmented soft body.

Ø  Large muscular foot modified for creeping, burrowing and swimming.

Ø  Body is enclosed in membranous structure or mantle secreting calcareous protective shells.

Ø  Bisexual animals.

Ø  Eg: Pila, Bivalvia, Snail, Octopus


Ø  Exclusively marine animals characterized by triploblastic.

Ø  They are coelomate.

Ø  They possess radial symmetry in larva and bilateral symmetry in adults.

Ø  Locomotion is done with the help of tube feet which is also used for food grasping.

Ø  Few animals are sessile in this phylum,

Ø  Calcareous skeleton is present which is made up of plates or spines.

Ø  Bisexual animals with separate sexes.

Ø  Eg: Aurelia (star fish), Sea urchin, Brittle star, Sea cucumber.

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Chordates are the most developed organism on this earth. Chordates includes vertebrata which further subdivided into five classes which starts from less developed aquatic pisces and ends in most developed terrestrial mammals


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