Animal Kingdom | Chapter 4 Notes

Animal Kingdom chapter 4 cbse, class 11 Biology notes. This cbse Biology class 11 notes has a brief explanation of every topic that NCERT Biology syllabus has.

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Animal Kingdom

All the animals are classified on the basis of arrangement of cells, body symmetry, nature of coelom, pattern of digestive, circulatory and reproductive system.

Every known species is classified into five kingdoms: phyla, Class, Order, Family, and Genus based on certain identifiable characteristic features.

One of the important forms of classification of animals is the presence or absence of the notochord. There are two major groups that exist, namely: Chordates and Non-chordates.

The notochord is a flexible rod made up of a material similar to cartilage. If an animal has a notochord it is classified as a chordate.

Animals without a notochord are Non-chordates. The rod-like elastic structure that supports the body. This phylum consists of a group of worm-like, marine species with an organ-system level of organization.

animal kingdom

Members of phylum :

Porifera, Coelenterata, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata and Chordata.

Classification of animal kingdom based on common fundamental features

Phylum – Porifera (Sponges)

  • Members of Phylum Porifera are known as sponges
  • They are mostly marine, asymmetrical and have cellular level of organization.
  • They have a water transport system. Water enters through Ostia (minute pores) into a central cavity called Spongocoel, from there it goes out through Osculum.
  • Nutrition, gaseous exchange and excretion occurs by pathway of water transport system.
  • Skeletons of this Phylum are made up of spicules or spongin fibres.
  • They reproduce asexually by fragmentation and sexually by gametes formation.
  • Fertilisation is internal and development of zygote is indirect.
  • Example– Sycon, Spongilla (freshwater spongilla)

Phylum – Coelenterata (cnidaria)

  • This Phylum are Aquatic, mostly marine, sessile or free-swimming, radially symmetrical animals.
  • They display tissue level of organization, diploblastic, coelomate with single opening.
  • They exhibit two types of body called polyp and medusa. A polyp is a fixed, sessile and cylindrical form, e.g Hydra, Adamsia
  • Medusa is free swimming, umbrella shaped, having gonads like Aurelia and Jelly fish.
  • In some cnidarians Obelia alternation of generation (metagenesis) exists. 
  • Polyp produces medusa asexually and medusa produces polyp sexually.
  • They have central gastro-vascular cavity which has a single opening called hypostome and surrounded by sensory tentacles
  • Cnidoblasts are present on the tentacles, which contain nematocysts
  • Digestion is extracellular and intracellular
  • Skeletal of corals have calcium carbonate 

Phylum – Ctenophora 

  • They are commonly known as the Sea Walnuts or Comb Jellies 
  • They are marine, exhibit tissue level of organisation, diploblastic and radially symmetrical and acoelomate
  • Eight rows of ciliated comb plates present externally
  • Their body bears eight ciliated comb plates 
  • present externally which helps in locomotion.
  • Their digestion is extracellular and intracellular
  • Bioluminescence is present in Ctenophores.
  • Sexual reproduction, fertilisation is external with indirect development
  • Examples: Ctenoplana, Pleurobrachia

Phylum – Platyhelminthes (flatworms)

  • They have a dorso-ventrally flattened body, bilaterally symmetrical, triploblastic, acoelomates with organs levels of organization.
  • Hooks and suckers are present in parasitic forms. 
  • Flame cells present in them help in osmoregulation and excretion.
  • Fertilisation is internal and indirect  development through many larval stages
  • They are hermaphrodite. Example- Taenia, Planaria, Fasciola.

Phylum – Aschelminthes

  • They can be free-living, aquatic, terrestrial or parasitic in plants or animals.
  • They have a round body in cross-section, bilaterally symmetrical, triploblastic, pseudocoelomate with organ system organisation
  • Their alimentary canal is complete with well-developed muscular pharynx.
  • They are Dioecious. Females are longer than male.
  • Example- Ascaris (roundworm), Wucheriria(filarial worm), Ancyclostoma.

Phylum – Annelida

  • They are aquatic or terrestrial, bilaterally symmetrical, segmented with organ system 
  • Their longitudinal and circular muscles help in locomotion
  • Aquatic Annelids like Nereis possess lateral appendages parapodia which help in swimming. 
  • Nephridia is present which helps in osmoregulation and excretion.
  • Neural system consists of paired ganglia connected to a double ventral nerve cord by lateral nerves
  • Their reproduction is sexual. Nereis is dioecious, earthworm and leeches are monoecious
  • Example- Pheretima (earthworm), Hirudinaria (Blood sucking leech).

Phylum – Arthropoda

  • They are the largest phylum of animals which includes insects. 
  • They have an organ system of organization. 
  • They are bilaterally symmetrical, triploblastic, coelomate
  • They are triploblastic, coelomate, bilaterally symmetrical 
  • Body is covered with a chitinous exoskeleton.
  • Their body consists of three regions: head, thorax and abdomen. They have jointed appendages (jointed feet). 
  • They respire through gills, book lungs or tracheal systems with an open circulatory system.
  • They excrete through malpighian tubules, sense organs, antennae or eyes. 
  • They are mostly dioecious, oviparous
  • Fertilisation internal, mostly oviparous.
  • Examples- Bombyx (silkworm), Apis (honey bee)

Phylum – Mollusca

  • They are terrestrial or aquatic, bilaterally symmetrical, organ level of organization, triploblastic and coelomate.
  • The body is divided into head, muscular foot and visceral hump. Also unsegmented and covered with a calcareous shell.
  • Feather-like gills are present between their hump and mantle. Respiratory and excretory functions are executed by these gills
  • Their mouth contains a file-like rasping organ for feeding called radula.
  • They are dioecious, oviparous with indirect development
  • Example- Pila, Octopus, Loligo (squid), Sepia

Phylum – Echinodermata

  • They are endoskeleton of calcareous ossicles
  • They are marine with an organ system of organization.
  • Their adults are radially symmetrical and larvae are bilaterally symmetrical
  • Their mouth is present on the ventral side and anus on the dorsal side
  • Water vascular system helps in locomotion, capture of food and respiration.
  • Their sexes are separate, fertilisation is external and development is indirect.
  • Example- Asterias (Star fish), Cucumaria (Sea cucumber), Antedon (Sea lily).

Phylum – Hemichordata

  • They are marine animals with an organ systems of organization, bilaterally symmetrical, triploblastic and coelomate animals.
  • Their body is cylindrical, composed of anterior proboscis, a collar and a long trunk.
  • Open circulatory system, respiration by gills, excretory organ is proboscis glands.
  • They respire through gills. They have an open circulatory system.
  • Proboscis gland works as an excretory organ
  • External fertilisation with indirect development.
  • Example- Balanoglossus, Saccoglossus.

Phylum – Chordata

They have notochord, have dorsal hollow nerve cord and paired pharyngeal gill slits.

They are bilaterally symmetrical, triploblastic, coelomate with organ system levels of organization.

They have closed circulatory system, ventral heart and post-anal tail 

They have three subphylums come under Chordata:

Urochordata: notochord is present only in the larval tail. e.g. Ascidia, Salpa, Doliolum

Cephalochordata: notochord is present from head to tail and persists throughout life e.g. Branchiostoma (Lancelet or amphioxus)

Vertebrata: notochord in present in embryonic period which is replaced by vertebral column in the adults.

Subphylum Vertebrata is further divided into two divisions Agnatha( lacks jaw) and Gnathostomata ( bears jaw).

Gnathostomata is further divided into two super classes- Pisces( bears fins) and Tetrapoda (bears limbs). Tetrapoda (bear limbs): four classes- Amphibia, Reptilia, Aves and mammals

Class I – Cyclostomata (Circular Mouthed Fishes)

  • There are ectoparasites on some fishes. They have a sucking and circular mouth without jaws.
  • Their body devoid of scales, 6-15 pairs of gill slits for respiration
  • Their cranium and vertebral column is cartilaginous.
  • They have closed type circulation. 
  • They are marine animals but they migrate to freshwater for spawning and die after a few days. Larvae return to the seas after metamorphosis.

Example– Petromyzon (Lamprey), Maxine (Hagfish).

Class II – Chondrichthyes (Cartilaginous fishes)

  • They are marine, have streamlined bodies, and have cartilaginous endoskeleton. Their mouth is on the ventral side.
  • They are cold blooded, and having tough skin with minute placoid scales.
  • Their gill slits are separate without an operculum.
  • The notochord is present throughout their life
  • Placoid scales are present on the skin which makes them tough
  • They swims constantly to avoid sinking as air bladders are absent
  • They have powerful jaws and are predators.
  • Their heart has two chambers, cold blooded (Poikilothermous).
  • They have separate sexes, Internal fertilisation, many are viviparous.
  • Special Electric organ is present in Torpedo and Poison sting in Trygon

Examples: Scoliodon (Dogfish), Trygon (Stingray), Pristis (Sawfish), Carcharodon (Great white shark)

Class III – Osteichthyes (Bony fishes)

  • They are marine and freshwater animals.
  • They have a bony endoskeleton and streamlined body with four pairs of gills covered by an operculum.
  • Their skin is covered with cycloid scales, air bladder is present, and their heart has two chambers, cold blooded.
  • Their sexes are separate, fertilisation external, oviparous and development direct.


Marine- Hippocampus (Sea horse), Exocoetus (Flying fish)

Fresh water- Labeo (Rohu), Catla ,Clarias (Magur).

Vertebrates Classification

There are five classes of vertebrates. These vertebrates comprise all the species of animals. They have developed vertebral columns as well as an internal skeleton.

There are more than 60,000 species of vertebrates identified under phylum Chordata. Their bodies are bilaterally symmetrical, coelomic, triploblastic, and with complex differentiation of body tissues and organs.

Five Classes of Vertebrates

  • Pisces
  • Amphibian
  • Reptile 
  • Aves
  • Mammal

Pisces (Fishes)

They are aquatic animals, having a pair of fins which are used for propulsion and movement. Fish are cold-blooded (except moon fish).

Skeletons may be cartilaginous or bony and their respiration occurs through gills. They do not possess eyelids because the surface of the eye is to be kept moist all the time.

Examples: Dogfish and Rohu.


They are cold-blooded organisms which require an aquatic habitat to lay eggs. They have two pairs of limbs, smooth and moist skin for respiration. 

They also have protruding eyes which are usually protected by more than one pair of eyelids. (Frogs have 3).

Examples: Frogs, Toads, and Salamanders.


They are ectothermic in nature (cold-blooded), characterized by osteoderms which form scales, bony plates or scutes on the skin.  

Reptiles don’t have external ears and some reptiles such as snakes are actually “deaf” but pick up vibrations through the ground.  

Snakes have one amazing sense which no other animal has, they possess Thermoception, which means that they can see infrared radiation emitted by objects or prey.

Examples: Tortoise, Wall lizard, Snake

Aves (Birds)

Most members of birds have a streamlined body specially designed to offer low air resistance during flight. 

Instead of forelimbs they have wings to fly with the power coming from breast muscles. Feathers help to flight, thermal insulation to water-proofing. 

They are warm-blooded and are able to regulate their body temperature. Aves have beaks for preening and feeding. 

Examples: Parrot, Pigeon, Duck


These animals are distinguished by the presence of mammary glands. They have two pairs of limbs for walking, grasping, swimming, flying, etc. 

Their skin is covered by hair and they have an external ear called pinnae. They are warm-blooded animals.

Examples: Monkeys, Lions, Bats, and Humans.

Press Here To Read Chapter 3: Plant Kingdom

Frequently Asked Questions

Q1. What are the types of Phylums are present?

Answer: Porifera, Coelenterata,Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata and Chordata.

Q2. What are vertebrates classes?

Answer: There are five classes: Pisces, Amphibian, Reptile, Aves, Mammal

Final Words

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