1. Levels of Organisation

All members of animalia are multicellular but all of them do not exhibit the same pattern of organisation of cells.

2. A complete digestive system has two openings, mouth and anus.

           ●Platyhelminthes has only a single opening to the outside of the body that serves as both mouth and anus, and is hence called incomplete.

3. Circulatory system may be of two types:

Open type in which the blood is pumped out of the heart and the cells and tissues are directly bathed in it and

Closed type in which the blood is circulated through a series of vessels of varying diameters (arteries, veins and capillaries).

4. Symmetry

Sponges are mostly asymmetrical, i.e., any plane does not divide them into equal halves.

When any plane passing through the central axis of the body divides the organism into two identical halves, it is called radial symmetry. Coelenterates, ctenophores and echinoderms have this kind of body plan

Animals like annelids, arthropods, etc., where the body can be divided into identical left and right halves in only one plane, exhibit bilateral symmetry

5. Diploblastic and Triploblastic Organisation

          Two embryonic layers, an external ectoderm and an internal endoderm, are called diploblastic animals, e.g., coelenterates.

            • An undifferentiated layer, mesoglea, is present in between the ectoderm and the endoderm

           Those animals in which the developing embryo has a third germinal layer, mesoderm, in between the ectoderm and endoderm, are called triploblastic animals (Platyhelminthes to chordates).


6. Coelom 

 Between the body wall and the gut wall  The body cavity

Lined by mesoderm

Animals possessing coelom  coelomates,

• e.g., annelids, molluscs, arthropods, echinoderms, hemichordates and chordates

if the body cavity is not lined by mesoderm, (the mesoderm is present as scattered pouches)  Pseudocoelom

• The animals possessing them are called pseudocoelomates,

o e.g., Aschelminthes

   The animals in which the body cavity is absent are called acoelomates,

o e.g., Platyhelminthes


In some animals, the body is externally and internally divided into segments with a serial repetition of at least some organs.

This pattern called metameric segmentation

Phenomenon is known as metamerism.

For example, in earthworm


Mesodermally derived rod-like structure

Formed on the dorsal side during embryonic development

Animals with notochord are called chordates

Animals which do not form this structure are called non-chordates, e.g., porifera to echinoderms. @sciencegajab


      Commonly known as SPONGES.

      Generally marine


       Primitive multicellular animals


●Sponges have a water transport or canal system.

    • Water enters through minute pores (ostia) in the body wall

     • A central cavity, SPONGOCOEL,

     • Water goes out through the osculum.

 This pathway of water transport is helpful in food gathering, respiratory exchange and removal of waste.
Choanocytes or collar cells line the spongocoel and the canals.

 Digestion is intracellular. 

 A skeleton made up of SPICULES OR SPONGIN FIBRES.

Sexes are not separate (hermaphrodite),

• i.e., eggs and sperms are produced by the same individual.

Sponges reproduce

• asexually by fragmentation

• sexually by formation of gametes.

• Fertilisation is internal

• development is indirect having a larval stage

• Larva is morphologically distinct from the adult.


• Sycon (Scypha),

• Spongilla (Fresh water sponge)

• Euspongia (Bath sponge)


 Aquatic, mostly marine,

Sessile or free-swimming,

 Radially symmetrical animals This content#sciencegajab 

The name cnidaria is derived from the cnidoblasts or cnidocytes

• Cnidoblasts or Cnidocytes (contain the stinging capsules or nematocytes) present on the tentacles and the body.

• Cnidoblasts are used for anchorage, defence and to capture prey


 Diploblastic. , mouth on hypostome.

Digestion is extracellular and intracellular.

 Some of the cnidarians, e.g., corals have a skeleton composed of calcium carbonate.

 Cnidarians exhibit two basic body forms called polyp and medusa

Polyp is a sessile and cylindrical form like Hydra, Adamsia, etc.

Medusa is umbrella-shaped and free-swimming like Aurelia or jelly fish.

 Those cnidarians which exist in both forms exhibit alternation of generation (Metagenesis), i.e., polyps produce medusae asexually and medusae form the polyps sexually (e.g., Obelia).


• Physalia (Portuguese man-of-war),

• Adamsia (Sea anemone),

• Pennatula (Sea-pen),

• Gorgonia (Sea-fan) and

• Meandrina (Brain coral).


Commonly known as sea walnuts / comb jellies

Exclusively marine,

This content  #sciencegajab 

Radially symmetrical,

Diploblastic organisms

Tissue level of organisation.

 The body bears eight external rows of ciliated comb plates, which help in locomotion

Digestion is both extracellular and intracellular.

 is well-marked in ctenophores.

Sexes are not separate.

 Reproduction takes place only by sexual means.

 Fertilisation is external with indirect development.

Examples: Pleurobrachia and Ctenoplana.


Dorso-ventrally flattened body, hence are called flatworms

 Mostly ENDOPARASITES found in animals including human beings.

Bilaterally symmetrical,

Triploblastic and acoelomate animals


Hooks and suckers are present in the parasitic forms.

Absorb nutrients from the host directly through their body surface.

 Specialised cells called FLAME CELLS help in osmoregulation and excretion.

 Sexes are not separate. @ sciencegajab 

Fertilisation is internal and development is through many larval stages.

Some members like Planaria possess high regeneration capacity.


• Taenia (Tapeworm),

• Fasciola (Liver fluke).


 Body is circular in cross-section, hence, the name roundworms

May be free living, aquatic and terrestrial or parasitic in plants and animals.
 Bilaterally symmetrical,
Triploblastic @sciencegajab PSEUDOCOELOMATE ANIMALS.

 Alimentary canal is complete with a well developed muscular pharynx.

An excretory tube removes body wastes from the body cavity through the excretory pore.

Sexes are separate (dioecious), i.e., males and females are distinct.

Females are longer than males.

Fertilisation is internal

Development may be direct (the young ones resemble the adult) or indirect.

Examples :

• Ascaris (Round Worm),

• Wuchereria (Filaria worm),

• Ancylostoma (Hookworm).


Aquatic (marine and fresh water) or terrestrial;

 Free-living, and sometimes parasitic.

 They exhibit organ-system level of body organisation a

Bilateral symmetry.


Coelomate animals.

 Their body surface is distinctly marked out into segments or metameres

• hence, the phylum name Annelida (Latin, annulus : little ring)

They possess longitudinal and circular muscles which help in locomotion.

Aquatic annelids like Nereis possess lateral appendages, PARAPODIA, which help in swimming.

 A closed circulatory system is present.

Nephridia (sing. nephridium) help in osmoregulation and excretion.

Neural system consists of paired ganglia (sing. ganglion) connected by lateral nerves to a double ventral nerve cord.

Nereis, an aquatic form, is dioecious,

 earthworms and leeches are monoecious.

 Reproduction is sexual.

 Examples :

• Nereis,

• Pheretima (Earthworm) and

• Hirudinaria (Blood sucking leech).


Largest phylum

 includes INSECTS (Most abundant animals)

 Over two-thirds of all named species on earth are arthropods

Organ-system level of organisation.

 Bilaterally symmetrical,


Segmented and Coelomate animals.

The body covered by chitinous exoskeleton.

The body consists of head, thorax and abdomen.

 They have jointed appendages (arthros-joint, poda-appendages) Respiratory organs are gills, book gills, book lungs or tracheal system.

 Circulatory system is of open type.

Sensory organs like antennae, eyes (compound and simple), statocysts or balance organs are present.

Excretion takes place through MALPIGHIAN TUBULES.

 They are mostly dioecious.

 Fertilisation is usually internal. 

They are mostly oviparous.

Development may be direct or indirect.


• Economically important insects –

o Apis (Honey bee), Bombyx (Silkworm), Laccifer (Lac insect)

• Vectors –

o Anopheles, Culex and Aedes (Mosquitoes)

• Gregarious pest –

o Locusta (Locust) Living fossil – Limulus (King crab).


Second largest animal phylum

Terrestrial or aquatic (marine or fresh water)

Organ-system level of organisation. @ sciencegajab 

 Bilaterally symmetrical, triploblastic and coelomate animals.

Body is covered by a calcareous shell

 unsegmented with a distinct head, muscular foot and visceral hump.

 A soft and spongy layer of skin forms a mantle over the visceral hump.

The space between the hump and the mantle is called the MANTLE CAVITY in which feather like gills are present.

• They have respiratory and excretory functions.

The anterior head region has sensory tentacles. The mouth contains a file-like rasping organ for feeding, called RADULA

 They are usually dioecious and oviparous with indirect development.


• Pila (Apple snail),

• Pinctada (Pearl oyster),

• Sepia (Cuttlefish),

• Loligo (Squid),

• Octopus (Devil fish),

• Aplysia (Seahare),

• Dentalium (Tusk shell) and

• Chaetopleura (Chiton).


 Have an endoskeleton of calcareous ossicles and, hence, the name Echinodermata (Spiny bodied).

All are marine

Organ-system level of organisation.

The adult echinoderms are radially symmetrical but larvae are bilaterally symmetrical. @sciencegajab

They are triploblastic and coelomate animals.

 Digestive system is complete

• mouth on the lower (ventral) side

• anus on the upper (dorsal) side.

 The most distinctive feature  the presence of water vascular system

• helps in locomotion, capture and transport of food and respiration.

An excretory system is absent.

 Sexes are separate.


Reproduction is sexual.

Fertilisation is usually external.

 Development is indirect with free-swimming larva.

Examples: This content developed by Biomentors classes online

• Asterias (Star fish),

• Echinus (Sea urchin),

• Antedon (Sea lily),

• Cucumaria (Sea cucumber) and

• Ophiura (Brittle star).


Placed as a separate phylum under non-chordata.

Small group of worm-like marine animals

Organ-system level of organisation.

 Bilaterally symmetrical, triploblastic and coelomate animals.

 The body is cylindrical

• composed of an anterior proboscis, a collar and a long trunk

Circulatory system is of open type.

Respiration takes place through gills.

Excretory organ is proboscis gland.

Sexes are separate.

Fertilisation is external; Development is indirect.

Examples: Balanoglossus and Saccoglossus.


Fundamentally characterised by the presence of 

• A Notochord,

• A Dorsal Hollow Nerve Cord And

• Paired Pharyngeal Gill Slits

Bilaterally symmetrical,



 Organ-system level of organisation.

 Possess a post anal tail

 Closed circulatory system.

20. Phylum Chordata is divided into three subphyla:

 Urochordata or Tunicata, Cephalochordata and Vertebrata.

21. Subphyla Urochordata + Cephalochordata  Protochordates
 Exclusively marine.

22. In Urochordata Notochord is present only in larval tail
Examples: Urochordata – Ascidia, Salpa, Doliolum;

23. In Cephalochordata  Notochord extends from head to tail region and is persistent throughout their life.
Examples: Cephalochordata – Branchiostoma (Amphioxus or Lancelet).

24. The members of subphylum Vertebrata

          Possess notochord during the embryonic period.

         The notochord is replaced by a cartilaginous or bony vertebral column in the adult.

          “all vertebrates are chordates but all chordates are not vertebrates”

           Besides the basic chordate characters,

                       • vertebrates have a ventral muscular heart with two, three or four chambers,

                      • kidneys for excretion and osmoregulation and

• paired appendages which may be fins or limbs.


All are ectoparasites on some fishes.

 Elongated body bearing 6-15 pairs of gill slits for respiration.

Cyclostomes have a sucking and circular mouth without jaws

 Their body is devoid of scales and paired fins.

 Cranium and vertebral column are cartilaginous.

Circulation is of closed type.

Cyclostomes are marine but migrate for spawning to fresh water.

 After spawning, within a few days, they die.

 Their larvae, after metamorphosis, return to the ocean.

Examples: Petromyzon (Lamprey) and Myxine (Hagfish).


Marine animals

 Streamlined body

Cartilaginous endoskeleton

Mouth is located ventrally. @ sciencegajab 

Notochord is persistent throughout life.

 Gill slits are separate and without operculum (gill cover).

 The skin is tough, containing minute PLACOID SCALES.

Teeth are modified placoid scales which are backwardly directed.

Their jaws are very powerful.

These animals are predaceous.

 Due to the absence of air bladder, they have to swim constantly to avoid sinking.

 Heart is two-chambered (one auricle and one ventricle).

Some of them have electric organs (e.g., Torpedo) and some possess poison sting (e.g., Trygon).

 They are cold-blooded (poikilothermous) animals, i.e., they lack the capacity to regulate their body temperature.

 Sexes are separate.

In males pelvic fins bear claspers.

 They have internal fertilisation and many of them are viviparous.


• Scoliodon (Dog fish),

• Pristis (Saw fish),

• Carcharodon (Great white shark),

• Trygon (Sting ray).


Both marine and fresh water fishes

 Bony endoskeleton.

 Streamlined Body. @sciencegajab

Mostly terminal mouth

 Four pairs of gills ; covered by an operculum on each side.

Skin is covered with cycloid/ctenoid scales.

Air bladder is present which regulates buoyancy.

Heart is two chambered (one auricle and one ventricle).

They are cold-blooded animals.

Sexes are separate.

Fertilisation is usually external.

They are mostly oviparous and development is direct.


• Marine – Exocoetus (Flying fish), Hippocampus (Sea horse);

• Freshwater – Labeo (Rohu), Catla (Katla), Clarias (Magur);

• Aquarium – Betta (Fighting fish), Pterophyllum (Angel fish).


Live in aquatic as well as terrestrial habitats

Most of them have two pairs of limbs.

Body is divisible into head and trunk.

Tail may be present in some.

The amphibian skin is moist (without scales).

The eyes have eyelids.

A tympanum represents the ear.

Alimentary canal, urinary and reproductive

tracts open into a common chamber called cloaca which opens to the exterior.

 Respiration is by gills, lungs and through skin.

The heart is three chambered (two auricles and one ventricle).

These are cold-blooded animals.

 Sexes are separate.

 Fertilisation is external.

They are oviparous and development is indirect.


• Bufo (Toad),

• Rana (Frog),

• Hyla (Tree frog),

• Salamandra (Salamander),

• Ichthyophis (Limbless amphibia)


 Creeping or crawling mode of locomotion (Latin, reptum, to creep or crawl).

Mostly terrestrial animals

Body is covered by dry and cornified skin, epidermal scales or scutes

Do not have external ear openings.

Tympanum represents ear.

Limbs, when present, are two pairs.

Heart is usually three-chambered, but four-chambered in crocodiles.

 Reptiles are poikilotherms.

 Snakes and lizards shed their scales as skin cast.

 Sexes are separate.

Fertilisation is internal.

 They are oviparous and development is direct.

Reptiles have adapted to produce an egg that offers more protection. Amphibian eggs lack shells and must be laid in water so they stay moist; reptile eggs, on the other hand, have hard shells to keep the embryos inside safe from the environment and from predators.


• Chelone (Turtle),

• Testudo (Tortoise),

• Chameleon (Tree lizard),

• Calotes (Garden lizard),

• Crocodilus (Crocodile),

• Alligator (Alligator).

• Hemidactylus (Wall lizard),

• Poisonous snakes –

o Naja (Cobra), Bangarus (Krait), Vipera (Viper).


The characteristic features  Presence of feathers

Most of them can fly except flightless birds (e.g., Ostrich).

 They possess beak

 The forelimbs are modified into wings.

The hind limbs generally have scales and are modified for walking, swimming or clasping the tree branches.

Skin is dry without glands except the oil gland at the base of the tail.

 Endoskeleton is fully ossified (bony)

Long bones are hollow with air cavities (pneumatic).

The digestive tract of birds has additional chambers, the crop and gizzard.

Heart is completely four chambered.

They are warm-blooded (homoiothermous) animals, i.e., they are able to maintain a constant body temperature.

 Respiration is by lungs.

Air sacs connected to lungs supplement respiration.

 Sexes are separate.

 Fertilisation is internal.

They are oviparous and development is direct.

Examples :

• Corvus (Crow),

• Columba (Pigeon),

• Psittacula (Parrot),

• Struthio (Ostrich),

• Pavo (Peacock),

• Aptenodytes (Penguin),

• Neophron (Vulture).


 Found in a variety of habitats – polar ice caps, deserts, mountains, forests, grasslands and dark caves.

 Adapted to fly or live in water.

The most unique mammalian characteristic is the presence of milk producing glands (mammary glands) by which the young ones are nourished.

They have two pairs of limbs, adapted for walking, running, climbing, burrowing, swimming or flying

 The skin of mammals is unique in possessing hair.

External ears or pinnae are present.

 Different types of teeth are present in the jaw.

Heart is four chambered.

They are homoisothermous.

Respiration is by lungs.

 Sexes are separate

 Fertilisation is internal.

They are viviparous with few exceptions

Development is direct.


• Oviparous-

o Ornithorhynchus (Platypus);

• Viviparous –

o Macropus (Kangaroo),

o Pteropus (Flying fox),

o Camelus (Camel),

o Macaca (Monkey),

o Rattus (Rat),

o Canis (Dog),

o Felis (Cat),

o Elephas (Elephant),

o Equus (Horse),

o Delphinus (Common dolphin),

o Balaenoptera (Blue whale),

o Panthera tigris (Tiger),

o Panthera leo (Lion).