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Animal Kingdom: Animal Classifications

Table of Content

Basis of Classification

Animals are classified based on coelom, body symmetry, patterns of digestive, circulatory or reproductive system etc.

  • Circulatory system can be open or closed.
  • Symmetry can be radial or bilateral.
  • Animals are also classified based on the embryonic layers. They can be diploblastic or triploblastic.
  • Presence or absence of body cavity is another basis for classification. They can be pseudocoelomate, acoelomate, or coelomate.
  • Another basis for classification is metamerism.

Classification of animals

Fig.1. The broad classification of Animlia based on common fundamental features

Invertebrates classification

Characteristics of invertebrates

  • Absence of vertebral column.
  • They are heterotrophic organisms.
  • They can have radial, bilateral, or spherical in symmetry.
  • They have open respiratory system with spiracles, trachea and tracheoles.
  • Reproduction occurs via partial sexual reproduction. Reproductive cells produce male gamete sperm and female gamete ova.
PoriferaKnown as sponges, cellular body organization, canal system, Choanocytes or collar cells,Spongilla, Sycon

Fig. 2 . Sycon

Coelenterata (Cnidaria)

Free swimming or sessile, Stinging cells known as Cnidoblasts or Cnidocytes, tissue skeleton composed of Calcium carbonate,

exist in two basic forms- Polyp and medusa


Adamsia, Physalia, Gorgonia, Meandrina

Fig. 3 .Physalia

CtenophoraRadially symmetrical and diploblastic, exhibit a property of BioluminescencePleurobrachia and Ctenoplana

Fig. 4 .Pleurobrachia


Known as flatworms,

acoelomate and triploblastic,

parasitic forms have suckers and hooks,

flame cells help in excretion


Fasciola (Liver fluke), Taenia (Tapeworm)

Fig. 5 .Taenia


Commonly known as roundworms,

bilaterally symmetrical,

triploblastic, Pseudocoelomate



Wuchereria (Filarial worms), Ascaris (Round Worm), Ancylostoma (Hookworm).


Fig. 6 .Wu chereria


Organ level of organization,

bilaterally symmetrical,


metamerically segmented,


closed circulatory system,

Nephridia which helps in excretion


Hirudinaria, Nereis, Pheretima

Fig. 7 .Hirudinaria


Largest phylum of kingdom Animalia,

organ level of organization,

bilaterally symmetrical,

segmented, triploblastic animals,

exoskeleton made up of chitin,

body is divided into head, thorax, and abdomen,

jointed appendages

respiratory organs found such as gills, book gills, book lungs or tracheal system, hemolymph is present,

Malpighian tubules are meant for excretion


Locusta (Locust), Anopheles, Culex and Aedes

Fig.  8 .Locusta


Aquatic or terrestrial,

organ level of organization,

bilaterally symmetrical,

triploblastic animals,

unsegmented body,

body is divided into head, muscular foot, and visceral hump, Mouth contains radula for feeding

indirect development and oviparous


Loligo (Squid), Pinctada (Pearl oyster), Chaetopleura (Chiton), Pila (Apple snail)

Fig. 9 .Loligo


Calcareous endoskeleton,

exclusively marine,

organ level of organization,

water vascular system,

no excretory organ,

separate sexes,

development is indirect


Cucumaria (Sea cucumber), Asterias (Star fish), Echinus (Sea urchin)

Fig. 10 .Cucumaria

Note: For the detailed study kindly refer to the content “Animal kingdom: Invertebrates”

Characteristics of vertebrates

  • Notochord found in chordates are replaced by vertebrae.
  • All basal vertebrates used gills for respiration, such as fishes. But higher vertebrates lack gills. Instead of gills they have lungs for respiration.
  • Central nervous system is hollow with dorsal nerve cord.
  • Vertebrates are only chordates with cephalization (brain is concentrated in head region).
  • All vertebrates have ventral, muscular heart with a closed circulatory system. Closed circulatory system is defined as a system in which blood flow in arteries, veins and capillaries.
  • Reproduction is usually sexual.
  • They are unisexual animals with a pair of gonads.
  • They possess two pairs of appendages.
  • Presence of paired pharyngeal gill slits.
  • They are bilaterally symmetrical.
  • They are Triploblastic animals.
  • They have true coelom so known as coelomate with well- developed organ system and organization.
  • They possess post anal tail at some or the other stages of life.
  • Kidneys are excretory organs which maintains the osmoregulation of the body.

Vertebrates classification

Phylum Chordata is divided into- Urochordata or Tunicata, Cephalochordata and Vertebrata.

Vertebrates classification are as follows-


Notochord persist,

Gill slits are present,

Presence of Placoid scales or Ctenoid scales,

separate sexes

Internal fertilization

generally viviparous


Carcharodon (Great white shark), Trygon (Sting ray), Scoliodon (Dog fish)

Pterophyllum (Angel fish), Hippocampus (Sea horse), Freshwater – Labeo (Rohu)


Fig. 11. Catla


aquatic as well as in terrestrial, two pairs of limbs, divided into head and trunk, skin is without scales, cloaca is the common opening of alimentary canal, heart is three chambered, sexes are separate.

Three subclasses of Amphibia are- Labrinthodontia, Lepospondyli and Lissamphibia.



Salamandra (Salamander), Bufo (Toad), Rana (Frog)

Fig. 12. Rana tigrina


Crawling mode of locomotion,

skin with epidermal scales or Scutes, without external ear openings,


sexes are separate, internal fertilization,

development is direct, oviparous in nature.

Subclasses of Reptilia are as follows- Anapsida, Parapsida, Diapsida and Synapsida


Crocodilus (Crocodile), Testudo (Tortoise), Alligator (Alligator), Hemidactylus (Wall lizard), Poisonous snakes – Naja (Cobra)

Fig. 13. Crocodilus


Presence of feathers, beak

forelimbs which are modified into wings, hind limbs serve for walking

presence of oil glands,

endoskeleton is bony, crop and gizzardheart is four chambered


lungs are respiratory organs.

There are basically two subclasses- Archaeornithes and Neornithes


Aptenodytes (Penguin), Neophron (Vulture), Corvus (Crow), Columba (Pigeon)


Fig. 14. Aptenodytes


Presence of milk producing glands known as mammary glands, possess two pairs of limbs,

presence of characteristics hairs, presence of external ear

heart is four chambered,


lungs are the respiratory organs,


fertilization is internal


Rattus (Rat), Canis (Dog), Felis (Cat), Macropus (Kangaroo), Pteropus (Flying fox), Camelus (Camel), Oviparous-Ornithorhynchus (Platypus)



Fig. 15. Members of Mammalia

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