Animal Kingdom: Complete Chapter Notes For Class 11 NEET by PW

Remembering the characteristic features, classifications and examples of different animal groups can become difficult when several phyla and classes have similar features. For NEET preparation, you need to identify the distinguishing characteristics of each group and recall the examples associated with them.

The PW Animal Kingdom Complete Chapter One-Shot Revision Video For Class 11 NEET brings the important classification concepts together for quick chapter revision. These notes can be used alongside the video to revise the major animal groups, their characteristics and important examples before practising NEET questions.

Basis Of Animal Classification

The six fundamental criteria used in animal classification are:

1. Levels Of Organization

2. Body Symmetry

3. Germinal Layers

4. Coelom

5. Segmentation

6. Notochord

These features help classify animals into phyla, classes, and superclasses.

Levels Of Organization

Animals show increasing complexity as cells become specialised and form tissues, organs, and organ systems.

• Cellular Level: Porifera lack true tissues. Individual cells perform basic functions such as nutrition, respiration, and excretion.

• Tissue Level: Cnidaria and Ctenophora contain specialised groups of cells forming tissues.

• Organ Level: Specific organs first appear in Platyhelminthes.

• Organ-System Level: This begins from Aschelminthes and includes Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata, and Chordata.

(*Memory Tip: Remember the progression as Cells → Tissues → Organs → Organ systems. Increasing complexity leads to greater specificity of function.)

Digestive System

An incomplete digestive system has a blind-sac plan. A complete system allows food to move in one direction from mouth to anus.

Circulatory System

Body Symmetry

A plane of symmetry divides an organism into equal mirror-image halves.

• Asymmetry: No plane divides the body into equal halves. Mostly Porifera are asymmetrical.

• Radial Symmetry: Several planes passing through the central axis produce equal halves. Adult echinoderms, many cnidarians, and ctenophores show this condition.

• Bilateral Symmetry: Only one plane divides the body into equal left and right halves. Platyhelminthes onward generally show bilateral symmetry, except adult echinoderms.

Echinoderms are bilaterally symmetrical as larvae but radially symmetrical as adults.

 (*Memory Tip: Radial symmetry allows multiple planes of division, while bilateral symmetry allows only one plane dividing the body into left and right halves.)

Germinal Layers

During embryonic development, cells differentiate and become specialised for particular functions.

Diploblastic Animals

Diploblastic animals possess two germinal layers:

1. Ectoderm: Outer layer forming the epidermis.

2. Endoderm: Inner layer forming the gut lining.

A jelly-like layer called mesoglea may occur between them. Cnidaria and Ctenophora are diploblastic.

Triploblastic Animals

Triploblastic animals possess:

1. Ectoderm

2. Mesoderm

3. Endoderm

The mesoderm lies between the ectoderm and endoderm and supports the development of complex structures such as muscles and bones. Triploblastic organization begins from Platyhelminthes.

Coelom

A coelom is a body cavity between the ectoderm and endoderm that is completely lined by mesoderm.

(*Memory Tip: A true coelom has a complete mesodermal boundary. A cavity alone does not make an animal coelomate.)

Segmentation And Metamerism

Segmentation is the division of the body into distinct external and internal segments. When organs are repeated serially in successive segments, the condition is called metameric segmentation or metamerism.

Every metameric animal is segmented, but every segmented animal is not necessarily metameric.

Annelida shows clear external and internal metamerism. Segmentation is also present in Arthropoda and Chordata.

Notochord And Chordates

The notochord is a mesodermally derived, rod-like structure on the dorsal side of the body. It provides support during embryonic development and separates the developing neural canal from the alimentary canal.

Animals possessing a notochord at any stage are called chordates. Animals without it are non-chordates.

All vertebrates are chordates, but all chordates are not vertebrates.

Important Non-Chordate Phyla

Porifera

Porifera are aquatic, mostly marine, pore-bearing animals commonly called sponges.

• Cellular level of organisation

• Mostly asymmetrical

• No true tissues or organs

• Intracellular digestion

• Sessile habit

• Skeleton made of silica or calcium carbonate spicules and spongin fibres

The characteristic water canal system includes:

1. Ostia: Water-entry pores

2. Spongocoel: Central cavity

3. Osculum: Exit opening

4. Choanocytes: Flagellated collar cells that maintain water flow

Asexual reproduction occurs through fragmentation and gemmules. Sexual reproduction involves internal fertilisation and indirect development.

Examples include Sycon, Euspongia, and freshwater Spongilla.

(*Memory Tip: Spicules act like protective thorns for a sessile sponge. Remember Spongilla as the freshwater representative.)

Cnidaria

Cnidarians are aquatic, mostly marine, diploblastic animals with tissue-level organisation and radial symmetry.

Their characteristic cells are cnidoblasts, which contain nematocysts. These stinging capsules help in:

• Defense

• Prey capture

• Paralyzing prey

• Attachment

The gastrovascular cavity has one opening that functions as both mouth and anus. Digestion is both extracellular and intracellular.

Cnidarians occur in two body forms:

• Polyp: Sessile and cylindrical, as in Hydra and corals.

• Medusa: Free-swimming and umbrella-shaped, as in Aurelia.

In metagenesis, the polyp produces medusae asexually, while the medusa produces polyps sexually. Obelia is a classic example.

Examples include Hydra, Aurelia, Physalia, Adamsia, Pennatula, and Gorgonia.

Ctenophora

Ctenophores are exclusively marine, diploblastic animals with tissue-level organisation.

• Mostly radial symmetry

• Eight rows of ciliated comb plates for locomotion

• Colloblasts for prey capture

• Bioluminescence in most members

• Only sexual reproduction

• External fertilisation and indirect development

Examples include Ctenoplana and Pleurobrachia.

Platyhelminthes

Platyhelminthes are dorsoventrally flattened flatworms.

• Bilateral symmetry

• Triploblastic

• Organ-level organisation

• Acoelomate

• Mostly endoparasitic

• Flame cells and protonephridia for excretion and osmoregulation

Parasitic forms possess hooks and suckers for attachment to the host. Digestion is incomplete in free-living forms and absent in some parasites. Reproduction may be monoecious or dioecious, with internal fertilization.

Examples include:

• Planaria: High regeneration

• Taenia: Tapeworm

• Fasciola: Liver fluke

Aschelminthes

Aschelminthes are roundworms with a circular cross-section.

• Bilateral symmetry

• Triploblastic

• Organ-system organisation

• Pseudocoelomate

• Complete alimentary canal

• Muscular pharynx

• Dioecious and sexually dimorphic

• Internal fertilisation and indirect development

Excretion may occur through flame cells, protonephridia, excretory tubes, or renette cells.

Important parasites include Ascaris, Wuchereria bancrofti, and Ancylostoma.

Annelida

Annelids are segmented worms with a true coelom and true metameric segmentation.

• Bilateral, triploblastic, and coelomate

• Closed circulatory system

• Nephridia for excretion

• Longitudinal and circular muscles for movement

• Setae or parapodia for locomotion

Earthworms are monoecious, while Nereis is dioecious. Examples include Pheretima, Nereis, and Hirudinaria.

Arthropoda

Arthropoda is the largest phylum and contains animals with jointed appendages and a chitinous exoskeleton.

• Bilateral, triploblastic, and coelomate

• Open circulatory system

• Segmented body

• Compound eyes and antennae

• Malpighian tubules in insects

• Internal fertilisation and mostly oviparous reproduction

Examples include honeybees, silkworms, mosquitoes, spiders, crabs, and Limulus. Culex, Anopheles, and Aedes transmit elephantiasis, malaria, and dengue, respectively.

Mollusca

Molluscs have soft, unsegmented bodies divided into the head, muscular foot, and visceral hump.

• The mantle covers the visceral hump.

• Mantle secretes a calcareous shell.

• The mantle cavity contains gills.

• Radula is used for scraping food.

• Most are dioecious.

Examples include Pila, Pinctada, Sepia, Loligo, Dentalium, and Aplysia.

Echinodermata

Echinoderms are exclusively marine animals with a calcareous endoskeleton and spines.

• Bilateral larvae and radial adults

• Complete digestive system

• Water vascular system

• Tube feet for locomotion, feeding, and respiration

• No specialised excretory organ

Examples include Asterias, Ophiura, Echinus, Antedon, and Cucumaria.

Hemichordata

Hemichordates are marine, worm-like, coelomate animals divided into proboscis, collar, and trunk.

They possess a stomochord, but it is not a true notochord. Therefore, they are non-chordates. Respiration occurs through gill slits, and the proboscis gland performs excretion.

Examples include Balanoglossus and Saccoglossus.

Chordata And Vertebrate Classes

Chordates possess:

• Dorsal, hollow, single nerve cord

• Notochord

• Pharyngeal gill slits

• Post-anal tail

• Ventral heart

• Generally closed circulation

Subphyla

1. Urochordata: Notochord present only in the larval tail; examples include Ascidia and Salpa.

2. Cephalochordata: Notochord extends from head to tail throughout life; example: Branchiostoma.

3. Vertebrata: Notochord is replaced by the vertebral column.

Major Vertebrate Groups

Animal Kingdom requires regular revision because the chapter includes numerous classification features, phyla, classes and examples. Focus on the distinguishing characteristics and representative examples of each group while revising. The PW Animal Kingdom Complete Chapter One-Shot Revision Video For Class 11 NEET can help you revise the important concepts quickly before practising NEET questions. 

NEET Resources  You Might Like:

• NEET Syllabus 

• NEET PYQs

• NEET Mind maps

• NEET Sample Papers

• NEET Diagrams

• NEET Formula