The most important characteristics of phylum chordata are:

1. They possess a notochord either throughout life or during early embryonic development.

2. Dorsal hollow nerve cord.

3. Paired gill slits on the lateral sides of pharynx.

4. Post anal tail.

5. Closed circulatory system.

Phylum chordata can also be divided as :


Sub-Phylum 1. Urochordata

They are exclusively marine.

(i) This sub-phylum is also called Tunicata because the adult body is enclosed within a leathery test or tunic formed of a cellulose-like organic substance termed tunicin.


(ii) The larva (Ascidian tadpole) undergoes retrogressive metamorphosis, i.e., change from better developed larva to less developed adult, e.g., Herdmania (Sea Squirt).

(iii) Vanadocytes are present except in Herdmania. Vanadium gives green colour to blood. Excretion by neural gland, hence excretion is glandular.

Examples: Salpa, Doliolum, Ascidia.

Sub-phylum 2. Cephalochordata


(i) The notochord extends upto anterior end of the body, hence this sub-phylum is named so.

(ii) The tail is present throughout life,e.g., Branchiostoma (Amphioxus).

Amphioxus / Branchiostoma has both ends pointed like lance. Hence it is commonly called lancelet.


(i) These are advanced chordates that have cranium (cartilage or bony brain box) around brain.

(ii) Notochord is present only in the embryonic stages, it is replaced by cartilaginous or bony vertebral column (back bone) in the adult forms. They have paired appendages as fins and limbs.

(iii) Closed circulatory system, muscular and ventral heart 2, 3 or 4 chambered, lymphatic system present, erythrocytes and haemoglobin are present.

(iv) A pair of kidneys are present for excretion and osmoregulation; endocrine glands are well developed; they are generally unisexual; have single pair of gonads.

Division 1 : Agnatha (The Jawless Vertebrates)

They are the most primitive of all craniates.

The mouth does not possess jaws hence named Agnatha.

Vertebral column is represented only by small imperfect neural arches over the notochord.

They do not have exoskeleton and paired appendages.

They have single nostril. Internal ear has one or two semi-circular canals.

They are cold blooded.

It includes 2 classes :

1. Ostracodermi 2. Cyclostomata

1. Ostracodermi:

Ostracodermi are all extinct now and are called fossil agnatha.

These were shell skinned with exoskeleton of bony plates. e.g. Cephalaspis.

They were the first jawless fishes (originated in Ordovician period in Palaeozoic era).

2. Cyclostomata: Its general characters are :

(i) All living members of the class Cyclostomata are ectoparasites on some fishes. The body is devoid of scales and paired fins. Head and brain are poorly developed. They are also called jawless fishes.

(ii) Cyclostomes have an elongated body bearing 6 -15 pairs of gill slits in their gill pouch for respiration and have a sucking and circular mouth .

(iii) Single sex organ discharges the gametes in the well developed coelom.

(iv) Cranium and vertebral column are cartilaginous with persistent notochord.

(v) Stomach is absent.

(vi) A single dorsal nostril leads into closed nasal sac. A functional pineal eye is present just behind it.

(vii) Circulation is of closed type.

(viii) Kidneys are mesonephric.

Differences between Lamprey and Hag fish


Concept Builder

1. Petromyzon , though marine, goes to fresh water for spawning i.e., anadromous. After spawning within a few days, they die.

2. Larva Ammocoete hatches out of eggs in about 14-21 days. Larval period may long from 3 to 7 years.

3. Ammocoete is connecting link between Amphioxus and the cyclostomes.

4. Lingual Cartilage is also a part of skeleton, that lies in the tongue region and supports it (Lingual = related to tongue).

5. Typhlosole is a fold of epithelium in the intestine. It prevents the rapid flow of food in the intestine and increases the absorptive surface area.


Division 2 : Gnathostomata (The Jawed Vertebrates)

It includes advanced vertebrates.

Embryonic notochord is usually replaced in adults by a vertebral column.

Paired fins or limbs are present.

Mouth has jaws hence it is named gnathostomata.

Paired nostrils are present.

Intemal ear has three semicircular canals. Girdles present.

Gnathostomata is divided into two super classes: Pisces and Tetrapoda.


It includes true fishes. All are aquatic. The body bears fins. They are cold blooded.

(i) Monocondylic skull, slimy glands present on skin.

(ii) Vertebrae are Amphicoelous type

(iii) Neck absent, no upper or lower eyelids, no tympanum (only internal ear is present). Each eye has a well developed nictitating membrane.

(iv) Heart-two-chambered (S-shaped), venous heart with sinus venosus and conus arteriosus.

(v) Both renal portal and hepatic portal system are found. Hypophyseal portal system is also present.

(vi) Respiration occurs typically by gills.

(vii) Scales mesodermal or dermal, embedded in skin.

(viii) Kidneys -Mesonephric, ammonotelic (sharks-Ureotelic).

(ix) Lateral line sense organs are present.

Super class Pisces is divided into three classes :

Class I. Placodermi. (Extinct)

It includes the earliest fossil fishes which lived in fresh water. Body had an external protective armour of bony scales or plates. Primitive jaws with teeth were present. Skeleton was bony. Fins were mostly formed of large spines, e.g., Climatius (Spiny Shark).

(i) They appeared in Silurian period, flourished in Devonian and Carboniferous and became extinct in Permian .

(ii) The name placodermi means "armoured fish" or "Plate skinned".

(iii) Both paired and unpaired fins were present. Caudal fin heterocercal.

(iv) Autostylic jaw suspension; gill slits are covered by operculum.

Class II. Chondrichthyes.

This class includes cartilaginous fish, e.g., Scoliodon (dog fish), Torpedo (electric ray) etc. Sharks are fast swimming predators, whereas, the rays and skates are stout, bottom living scavengers and mollusc feeders.


Class III. Osteichthyes.

It includes bony fish, e.g., Labeo, Hippocampus, Exocoetus, Catla, Clarias, Betta, Pterophyllum etc.

Differences between cartilaginous and bony fishes

Some Important Fishes

Torpedo (Electric Ray) :

Torpedo is bottom dwelling, carnivorous fish. It stuns or kills the prey and enemies with electric shock from its electric organs. The latter are modified muscles. The skin is scale less.

Pristis: (Saw fish)

Head bears a series of strong tooth like denticles along the margin.

(a) Freshwater Species (b) Marine Species

Some air breathing fishes, use their paired fins to move on land and gave rise to the first land vertebrates. A living fossil of this group is Latimeria, a lobe-finned fish.

Exocoetus (Flying Fish) :


It does not fly but often leaps into the air upto about six metres high. The pectoral fins are modified into wing-like structures, with the help of which the fish glides.

Hippocampus (Sea Horse) :

The neck and the head of the fish are horse like and the tail is prehensile. The male bears a brood pouch in which the female lays eggs and the latter remain there till they hatch.

Labeo (Rohu) :

Labeo rohita and Labeo calbasu are the common fresh water edible carps. It is covered by large overlapping scales.


Clarias (Cat fish/Magur) :

Indian Cat Fish (Clarias batrachus) lives in ponds. It is carnivorous. The head bears sensory threads called barbels. The body is smooth and without scales. Other fresh water cat fishes of India are Mystus seengala (slinghara), Rita lita and Wallago attu (Malli).

Latimeria chalumnae (The Coelacanth) :

It was first caught in 1938 off the east coast of South Africa. It swims by curious rotating movements of its pectoral fins. All its fins except the anterior dorsal are lobed. It is the oldest living fish; and has survived till today without undergoing any change in it. It is therefore described as a living fossil.


Lung Fishes: Sub-Class Dipnoi

There are three genera of living lung fishes: Neoceratodus, Lepidosiren and Protopterus. All have three chambered heart (two auricles and one ventricle).

4. Fins:

(i) Paired pectoral and pelvic fins: Act as balancers and brakes; provide lift and counteract pitching and rolling.

(ii) Anterior dorsal fin : Counteracts rolling and yawing.

(iii) Posterior dorsal and anal fin : Counteract yawing and rolling.

(iv) Caudal fin : Propels the body and provides lift.

Concept Builder

Types of caudal fins :


(a) Diphycercal or Protocercal : Most primitive kind of tail fin. The tail is symmetrical, both externally and internally as in protocercal but it is secondarily symmetrical.

(b) Heterocercal/Hypocercal tail: Epicaudal and hypocaudal lobes are of unequal sizes.

(c) Homocercal: Identical lobes. Externally symmetrical and internally asymmetrical.

Endothermic fishes: Although most fishes are ectothermic, a few species, such as blue fish tuna and swordfish are able to maintain a body temperature higher than the temperature of the water that surrounds them. Genetic studies of these endotherms have revealed that the ability to maintain high body temperature gives these fishes an adaptive advantage by allowing them to hunt in much colder waters than their competitors.

Fish taken out of water dies of suffocation due to lack of oxygen. This is because the gill filaments stick together when taken out of water, thereby reducing the surface area.

Word Roots and Origin : Operculum from the Latin meaning "Gover".

5. Scales:

(i) Cosmoid : Absent in living fishes; consists of four distinct layers -outermost ganoine, followed by cosmine, spongy bone and innermost compact bone e.g. extinct fishes.

(ii) Placoid: Backwardly directed spine arising from a basal plate e.g. chondrichthyes only.

(iii) Ganoid or rhomboid scales are thick, diamond or rhomboid shaped plates e.g. primitive bony fishes like Acipencer etc.

(iv) Cycloid: Thin, flexible, circular in outline, marked with concentric lines of growth which can be used for determining age e.g. lung fishes, Amia etc.

(v) Ctenoid: Bear numerous small comb like spines e.g. higher bony fishes like perch etc.

6. Air bladder is associated with respiration, hydrostasis, sound production and audition.

7. Parental care :

(i) Nest building: e.g., Gasterosteus, Amia (bow fin), Protopterus, Lepidosiren (nest is built by males of these fishes).

(ii) Shelter in mouth: e.g., Males of cat fish, Arius.

(iii) Brood pouch: e.g., Male Hippocampus

Common Food Fishes Of India

False Fishes

Concept Builder

1. Stone fish is the most poisonous fish.

2. Gambusia fish (Iarvivorous) was introduced into several tropical regions to control malaria.

3. Catadromous fishes live in fresh water and go down to sea for breeding e.g., Anguilla (european eel). When fishes migrate from the rivers to the sea, it is called catadromous migration.


4. Anadromous fishes live in sea water and move to the rivers for breeding e.g., Hilsa, Salmon. When fishes migrate from sea to the rivers, it is called anadromous migration.

5. Hilsa is the only Indian fish that migrates from the seas to the river for breeding.

6. Most primitive fish (fossil): Climatius (Placodermi).

7. Anabas (climbing perch). It has accessory respiratory organs for breathing atmospheric air which enables the fish to take long overland excursions in search of earthworms.

8. Pomfret is the most widely eaten fish in India.

9. Dipnoi have incompletely divided three chambered heart.

10. Urinary bladder is absent in fishes.

11. Some elasmobranchs retain urea in blood to maintian hypertonicity.

12. Ampulla of Lorenzini are thermo receptors.

13. Electric organs of electric ray are modified muscles.

14. Bioluminescent fishes : Anamalops, Porichthyes etc.; Sound producing fishes: Mola, Batistes.

15. Poisonous glands are found in sting ray, eagle ray, Chimaera, Diodon and Tetrodon.

16. Fish byproducts are -Fish meals and fertilizers; fish flour, fish proteins, fish oil, steaming. Floatations, shagreen, fish glue, isinglass, leather, artificial pearls etc.

17. Weberian Ossicles were discovered by Waber (1820). These connect air bladder with internal ear.

18. Commercial name of integument of Scoliodon is "shagreen".

19. Typical trunk vertebrae of fish are amphicoelous, centrum peculiar as is supported by four wedge shaped calcified fibrocartilages forming a "Maltese Cross" and leaving uncalcified area.

20. The study of fish is called Ichthyology.

21. The study of skates, rays and sharks is called Torpedology.

22. Crossopterygians (Rhipidistia -Osteolepis genus) gave rise to amphibia.

23. Parental care is well developed in Hippocampus.

24. Isinglass is a gelatinous product obtained from the air bladders of certain fishes such as carps, salmons, cat fishes etc. It is used for making cements, jellies and for clarification of wines and beers.

25. Types of vertebrae :



All gnathostomes excluding fish are included in this super-class.

Typically all tetrapods (Gk. Tetra = four + podos = foot) possess two pairs of limbs. Skin is adapted to withstand exposure to air.

They have lungs for aerial respiration. Their sensory organs are adapted for reception in air, such as vision, hearing, smelling etc.

Tetrapoda is divided into four classes: Amphibia, Reptilia, Aves and Mammalia.

CLASS : AMPHIBIA - The Vertebrates with Dual-life (Gk. Amphi = two or both; bios = life)

General Characters:

There are about 3,000 species of amphibians out of which 2,600 species are in order Anura.

They are present in the warmer regions of the world except Newts and Salamander which are present in cooler regions.

They occur only in fresh water and moist land. Amphibians are not found in sea water.

The other characters are :

1. They are poikilothermal animals. They are amphibious in nature, i.e., they can live on land as well as in water. They are mostly found in warm countries. They are ectothermic (cold blooded). Body is divisible into head and trunk. Tail may be present in some forms.

2. The skin is smooth or rough, having cutaneous glands which keep it moist. They are usually without scales, but if scales are present, they are hidden beneath the skin (e.g., Caecilians).

3. Two pairs of limbs are used for locomotion.

4. The gills are present at least in the larval stage; some adult forms also carry them in addition to lungs (e.g., Necturus).

5. Alimentary canal, urinary and reproductive tracts open into a common chamber called cloaca which opens to the exterior.

6. Skull is dicondylic, i.e., with two occipital condyles for articulation with vertebral column.

7. The respiratory organs are lungs, buccopharyngeal cavity, skin and gills.

8. The heart is three chambered, having two auricles and one ventricle. In the heart, there are present sinus venosus and truncus arteriosus. Both hepatic portal and renal portal systems are well developed.

9. Kidneys are mesonephric. Urinary bladder is present in frog. Larvae and tailed amphibians (e.g., Salamanders) are ammonotelic. Frogs and toads are ureotelic.

10. Ear consists of internal and middle ear. Tympanum (outer membrane) covers the middle ear. The middle ear has a single ear ossicle called Columella Auris.

11. Ten pairs of cranial nerves are present. Sexes are seperate, fertilization is external, oviparous and development indirect.

12. They return towaterfor breeding. Male lacks copulatory organs. Indirect development occurs. A fish like stage, the tadpole is present.

13. Male frog can croak louder than females because of the presence of vocal sacs.

Example : Bufo (Toad), Rana (Frog), Hyla (Tree frog), Salamandra (Salamander), Ichthyophis (Limbless amphibia).

Living Amphibians are divided into three orders:


Concept Builder

1. Some frogs have developmen in amazing ways to prevent their eggs from drying out: The female surinam toad of South America carries her eggs in pits/pockets of skin on her back. As many as 60 young pass through the tadpole stage while embedded in her back and then emerge as small frogs.

2. In Frogs, external ears are absent, only Tympanum is seen externally: Frogs have a tympanic membrane on the surface of both sides of their head. The tympanic membrane of a human are called eardrums and each is protected inside ear canal.

3. Word Roots and Origins

(i) Caudata: from latin Caudata meaning "tail"

(ii) Nictitating: from the latin, nictare meaning to "wink"

Concept Builder

1. Seymouria is a connecting link between amphibia and reptiles.

2. Paedogenesis: Development of gonads and/or production of young ones by immature or larval forms e.g. Salamander (Ambyostoma).

3. Total neoteny is shown by Necturus, Siren and Proteus.

4. Toads are used in chinese medicines. Skin of toad secretes a substance that increases B.P when injected into humans.

5. Skin of tadpole secretes an enzyme, diastase.

6. Upper jaw of frog is derived from quadrate cartilage whereas lower jaw is derived from Meckel's cartilage.

7. First toe is called hallux.

8. Jaw suspension is autostylic, urostyle is last component of vertebral column.

9. Shapes of 2-7th vertebrae-Procoelous (typical); 8th vertebra-Amphicoelous; 9th vertebra - Acoelous.

10. Amphiuma-has the largest RBCs among vertebrates.

11. At the time of metamorphosis, the tadpole does not feed.

12. Blind worms (limbless amphibians) are unusual amphibians as only one species lives in water. All the other burrow underground and are rarely seen on the surface. Many do not even need water to breed.

13. Carboniferous Period-UAge of Amphibians".

14. The Arrow poison frogs secretes a powerful poison from the skin which can cause instant death.

15. Most poisonous frog-Golden dart poison frog from South America is the most poisonous frog. One adult frog contains enough poison to kill 200 people.


Their name refers to their creeping or crawling mode of locomotion.

Reptiles are cold blooded or poikilothermic animals.

There are only about 6,000 species of reptiles now living.

But fossils show that 200 million years ago, the reptiles were the most dominant animals on earth.

Herpetology is the study of reptiles.

The largest reptiles today are the 'komodo dragon' Varanus komodoensis of indonesia (a lizard) 3m in length, crocodiles (upto 7m), pythons (upto 10m) and giant tortoises weighing upto 600kg.

Important characters of this class are:

1. They are covered by dry and cornified skin having epidermal scales or scutes. Snakes and lizards shed their scales as 'skin cast'. Scales prevent loss of body water and so reptiles do not require a moist environment like amphibians.

2. Respiration is only through lungs, which is improved by the development of ribs.

3. Limbs -when present are two pairs, pentadactyl, digits have horny claws.

4. Mouth is terminal with conical teeth which are pleurodont in lizards and snakes and thecodont in crocodiles. Teeth are absent and replaced by horny beaks in turtles.

5. Endoskeleton is bony, skull is monocondylic (with one occipital condyle).

6. Heart is usually 3-chambered or partially 4-chambered. Interventricular septum is incomplete. Heart is completely 4-chambered in crocodiles. Two systemic arches are present. Erythrocytes are oval and nucleated.

7. Kidneys are metanephric. Excretion is uricotelic. 'Urinary bladder is absent in snakes and crocodiles.

8. Cranial nerves are 12 pairs. Jacobson's organ (vomeronasal organ) present in the roof of buccal cavity, concerned with smell, is well developed in snakes and lizards. They do not have external ear openings. Tympanum represent ears.

9. Sexes are separate. Males usually have a muscular copulatory organ. Fertilization is internal. Mostly are oviparous and development is direct. Some are viviparous. No metamorphosis.

Example : Chelone (Turtle), Testudo (Tortoise), Chameleon (Tree lizard), Calotes (Garden lizard), Crocodilus (Crocodile), Alligator (Alligator). Hemidactylus (Wall lizard), Poisonous snakes – Naja (Cobra), Bangarus (Krait), Vipera (Viper) etc.

(a) Chameleon (b) Crocodilus (c) Chelone (d) Naja


Classification of reptiles is based on temporal fossa on skull. The class reptilia is first divided into 5 sub-classes:

I. Anapsida, II. Euryapsida, III. Parapsida, IV-Synapsida and

V. Diapsida
Out of 5 sub-classes, the living reptiles are found only in two sub-classes,

[A] Anapsida and [B] Diapsida.

Concept Builder

1. Snake Charming :

Contrary to general belief, the snake charmer's cobra does not dance the tune of the flute.

Rather it follows the movement of the tip of the flute and the swaying body of its master, who really moves with the rhythm of the music.

Raising its head and spreading its hood, the cobra gets ready to strike the moving flute tip.

The charmer knows the striking distance and adjusts himself so that the snake orients towards the waving flute but keeps beyond the strike distance.

2. Rattle snake muscles :

Rattle snakes have the quickest moving skeletal muscles in the animal world.

Their tail muscle allows them to shake their rattle 90 times each second.

Most muscles would quickly tire from this kind of energetic activity, but the rattle snake can shake its tail for long periods of time.

The muscle's ability to use ATP in an efficient manner allows it to sustain a high level of activity.

Identification of poisonous and non-poisonous snake

Order: Crocodilia

Differences between Crocodile, Alligator and Gavialis


Concept Builder

1. Benadryl is used as an antidote to counteract the effect of haemotoxins.

2. Seymouria is considered as connecting link between amphibians and reptiles.

3. Mesozoic era is known as 'age of reptiles.'

4. Loreal pit of pit viper is thermoreceptor organ.

5. Reptiles without urinary bladder-snakes, crocodiles, alligators.

6. Many sea snakes are viviparous. Pit vipers are also mostly viviparous.

7. The oldest living animal in any Indian Zoo is the Aldabra giant tortoise.

8. Rattle snakes's tail emits a frightening sound which scares away the enemy.

9. The king cobra of India is the only snake in the world that builds a nest.

10. Largest snake-python; Smallest snake-Thread snake.

11. Largest lizard-Komodo dragon; Smallest lizard-Two species of dwarf gecko.

12. Long dinosaur-Diplodocus; Small dinosaur-Compsognafhus.

13. Largest living reptiles (i) Python, (ii) Crocodile (iii) Komodo dragon.

14. Hemidacfylus or wall lizard (Gecko) is a swift runneron smooth vertical surface due to the presence of vaccum pads.

15. Draco is flying lizard but it actually does not fly.

16. Heloderma is a poisonous lizard. (Gila monster)

17. Ophiosaurus known as 'glass snake', 'blind worm', or 'slow worm', limbless lizard.

18. Anguis is also blind worm and limbless.

19. Most Poisonous snake of world-Peninsular Tiger Snake.

20. Poisonous sea snake-Hydrophis

21. Heaviestdinosaurs-Brontosaurus

22. Biggestflesh eater dinosaur-Tyrannosaurus

23. Horned dinosaur-Stegosaurus

24. Varanus-Monitorlizard (largest living lizard).

25. Carapace is hard shield like structure present on the dorsal surface of tortoise and turtle.

26. Reptiles arose in the lower carboniferous time, from Labyrinthodon Amphibia.

27. Varanus is commonly called "Goye" or "monitor"; semi-aquatic; slightly laterally compressed tail.

28. Phrynosoma is found in deserts; called "Horned toad", skin hygroscopic; takes water in the form of dew; exudes red blood-like stream from eyes, whenever, terrified.

29. Iguana is 5-6 feet long; body and tail laterally compressed; arboreal in habit; herbivorous found in tropical America.

30. Sphenodon is the only living genus of Rhynchocephalia. It is commonly called Tuatara. Found only in New Zealand. It is called a living fossil as it resembles with Hanaesaurus of Jurassic age.


31. Largest living carnivorous reptile is Crocodilus.

32. Thermomorpha is a group of reptiles which are considered to be the ancestors of mammals.

33. Hedonic glands present in males secrete a sticky substance which hardens like spine and helps to hold the mate firmly.

34. Hemipenes-In Uromastix, cloaca possesses a pair of copulatory organs called hemipenes.

35. Russel's viper is the largest Indian viper.

36. Hafkin's Institute of Bombay is the main centre where antivenom is produced.

37. Limbs of Chameleon show syndactyly (fusion of digits) as an adaptation to arboreal life to form opposable finger to hold the twigs.

CLASS : AVES (Birds)

Study of birds is ornithology.

General Characters :

1. Birds are feathered bipeds, air breathing, truly flying veliebrates (other being bats from Class Mammalia).

2. Jaw bones are prolonged into a toothless beak or bill.

3. Limbs are two pairs. Forelimbs are modified as wings for flying. Hindlimbs or legs are large, each foot usually bears four, clawed toes. Hind limbs generally have scales.

4. Exoskeleton consists of feathers, scales and claws, which are epidermal derivatives. Skin without glands, the only cutaneous gland is uropygial gland or preen gland/oil gland at the base of tail.

5. Oesophagus is dilated into a crop for quick feeding and storage. Crop secretes 'pigeon millt' during breeding season. Stomach is divided into a glandular proventriculus and a muscular gizzard. The junction of small intestine and rectum is marked by a pair of rectal caecae. Cloaca of birds is three-chambered: antenior coprodaeum, middle urodaeum and a large posterior proctodaeum. There is no gall bladder in birds like pigeon.

6. Respiration with compact, spongy, nondistensible lungs continuous with thin walled air sacs. Air sacs reduce body weight, helps in double respiration and internal cooling. Larynx without vocal cords. A sound box or syrinx producing voice, lies at or near the junction Furcula of trachea and bronchi.

7. Heart is completely four-chambered as in mammals. Sinus venosus absent Only right aortic (systemic) arch persists in the adults. Renal portal system is vestigial. Erythiocytes are minute, oval and nucleated. The blood of the birds may be called the richest blood in the animal kingdom. It has more RBCs per cubic mm of blood than in any other animal.

8. Kidneys metanephric and three-lobed. Ureters open into cloaca. Urinary bladder is absent. Excretion is uricotelic.

9. Cranial nerves are 12 pairs.

10. Olfactory organs are poor. Middle ear contains a single ossicle. Eyes possess nictitating membrane, Pecten is a comb-like structure found in the eyes near blindspot. Pecten helps in the nutrition of eyeball. Pecten is found in all birds except Kiwi.

11. Sexes separate. Some birds show sexual dimorphism (e.g. , Parrot and Peacock). Male bird has a pair of abdominal testes and a pair of sperm ducts. A copulatory organ is absent in all birds except in ratitae, geese, ducks etc. Females are oviparous with a single (left) functional ovary and oviduct (Mullerian duct). Development is direct.

Different parts of oviduct secrete the following :

Ostium – Dense albumin

Magnum – White albumin

Uterus – Calcareous shell

Eggs of birds are cleidoic (with calcareous shell), macrolecithal (amount of yolk), meiolecithal (distribution of yolk). Extraembryonic membranes are present (Amniota).

12. Feathers are found only in birds. Feattlers are made up of a protein keratin and are water proof due to the oily secretion of preen glands. The arrangement of feathers on the body of birds is called Pterylosis. The featherless areas are called as Apteria. Four types of feathers are: quill feathers, contour feathers, filoplumes and down feathers. In absence of down feathers the birds will not be able to keep the body warm. Quill feathers in the wings are called 'remiges'. Quill feathers in the tail are called 'rectrices'. Filoplumes and Down feathers help in the insulation of the body.

13. Birds are the first vertebrates to have warm blood. Body temperature is regulated (homoiothermous).

14. Alaspuria -bastardwing -Feathers on 1st digit (thumb).

Example : Corvus (Crow), Columba (Pigeon), Psittacula (Parrot), Struthio (Ostrich), Pavo (Peacock), Aptenodytes (Penguin), Neophron (Vulture).

(a) Neophron (b) Struthio (c) Psittacula (d) Pavo

Concept Builder

Types of Feathers

1. Quills:

(a) They are large feathers found in wings and tail.

(b) It has a central axis called shaft.

(c) Small proximal part of the shaft is hollow, translucent and cylindrical and is termed as calamus.

(d) The long-distal, solid and opaque part of the stem is known as rachis.

(e) An umbilical groove extends all along the ventral side of rachis.

(t) Small hole on the proximal end of calamus is known as inferior umbilicus, the hole on the distal end of calamus is known as superior umbilicus.

(g) Each vane is composed of parallel filaments, the barbs. Each bears barbules.

(h) The distal barbules of each barb bear small hooklets.

(i) Emu bird have an after shaft as long as the main shaft.

Kinds of feathers. A and B-Quill, C-Contour, D-Filoplume, E-Down, F-Rictal bristle

2. Coverts are small feathers found in the wings and tail. They fill up the gaps left between the bases of the quills. They have short calamus in comparison to quills.

3. Contours: Small feathers that cover the body and give it its shape. They resemble the quills but their barbs are not so strongly joined and can be separated easily.

4. Filoplumes: Occur beneath contour feathers, very small in size, consists of long rachis bearing at the tip a few weak free barbs with barbules.

5. Down feathers/Nestling downs: They cover the newly hatched bird. They consist of short calamus, reduced rachis bearing flexible barbs with short barbules. They are found beneath contours.

6. Bristles: Short calamus, a long rachis bearing a few vestigeal barbs at its base. Bristles occur nearthe mouth in fly-catchers.

7. The first digit of the hand (thumb or pollex), bears a tuft of small feathers known as bustard wing or alaspuria or false wing.


Class Aves is divided into two sub-classes: Archaeornithes and Neornithes.


Sub-class I : Archaeornithes

1. All extinct Jurassic period birds of Mesozoic era.

2. Wings primitive with little power of flight.

3. Tail long, lizard-like with two lateral rows of rectrices.

4. Hand with clawed fingers.

5. Skull with teeth in both jaws e.g., Archaeopteryx.

Sub-class II : Neornithes

1. Modern as well as extinct, post-Jurassic period birds.

2. Wings well developed and adapted for flight (with few exceptions).

3. Tail short and reduced.

4. Teeth absent except in some fossil birds.

5. Sternum with keel or carina.

There are four super orders in this subclass :

Super-order I : Odontognathae


e.g., Hesperornis (with teeth) extinct.

Super-order II : Palaeognathae (Ratitae)

e.g., Flightless running birds

Super-order III : Impennae

e.g., Penguins (Aptenodytes)

Penguins are found in Antarctica (South pole). They have paddle-like wings and cannot fly. Penguins are marine and lay eggs in ice.

Super-order IV : Neognathae (Carinatae)

e.g., Modern flying birds as Columba (pigeon), Psittacula (parrot), Neophron (vulture), Pavo (peacock).

Conceptual Questions

Q.1 Why might it be a disadvantage for an eagle to have a urinary bladder?

Q.2 Why might teeth be a disadvantage to a bird?

Ans. 1. Urine contains a greater amount of water, which is heavy. The extra weight would be a disadvantage in flight.

2. Teeth are heavy and require heavy jaws.

Concept Builder

1. Brood Parasite : Eudynamis (koel, kokila). The male sounds like kuoo-kuoo-kuoo. The female is generally heard during breeding season and has short and sharp call kik-kik-kik, otherwise she is mostly silent. It does not make any nest but lays eggs in the crow's nest. In this way koel is nest parasite. Male is black. Female is brown and profusely spotted barred with white Koel is known as the Indian nightingale because of its pleasant sound.

2. Eagle-Eyes: Eagles have much better vision than humans do. The birds keen eyesight allows it to see prey at great distances. Its visual acuity is 3-4 times higher than ours.

Differences between Ratitae and Carinatae

Concept Builder

1. Largest bird-Struthio camelus -8 feet height, 300 Lbs weight.

2. Smallest bird -Mellisuga helenae-5.5 cm long.

3. Smallest egg of bird-Mel/isuga (Humming bird).

4. The humming bird is the only bird which can fly backward as well as forward.

5. Largest egg of bird-Struthio-1.5 Litre capacity.

6. Largest sea bird-Diomedea epomorphora (Royal albatross) wing stretch 200-375 cms.

7. Deepest Diver bird-Aptenodytes torsteri (Emperor Penguin)

8. Fastest Swimmer bird-Pygoscelis papua (Penguin)

9. Fastest Runner bird-Struthio-60 kms/hr. speed.

10. Heaviest bird of prey-Vulture gryphus.

11. Fastest Flying bird-Swift-rarely touch the earth.

12. Second largest bird is Emu (Dromaeus) as is most primitive living bird.

13. Recently extinct bird is Dodo (Passenger birds) of Mauritius.

14. Incubation period of Hen's egg at 102°F (38.8°C) is 21 days.

15. Though polygamy is common in birds, Emu is strictly monogamous.

16. Penguins are flightless birds found in Antarctica, wings are paddle-like, act as flippers during swimming and are covered by scale-like feathers.

17. T.H. Huxley said "birds are glorified reptiles". The feathers are highly modified reptilian scales. Birds have scales on their legs. Their eggs resemble reptilian eggs in general but have a calcareous shell.

18. Among the Indian birds the sun birds are probably the smallest.

19. The Bursa Fabricii is a blind sac with much lymphoid tissue in the cloaca of some young birds. It produces lymphocytes (a type of white blood corpuscles). It is also called "cloacal thymus".

20. Columbia has the world's richest diversity of birds. '.

21. Uropygium (tail)-the projecting terminal portion of a bird's body from which the tail feathers arise.

22. Swifts use saliva for binding nest materials.

23. Kiwi lays the largest egg in proportion to its own size.

24. Himalayan Bearded Vulture is the largest Indian bird. Previously the Sarus was considered the largest Indian bird.

25. Ostrich has the largest eyes of any land animal.

26. Kiwi is the only bird known to use the sense of smell for finding food on the ground.

27. Indonesia has the most bird species facing extinction.

28. Red Billed Quelea (Quelea quelea) of Africa are the most abundant birds. Previously the house sparrow was considered the most abundant species of birds.

29. Jatinga is a village in Assam where a mass suicide of birds occurs.

30. The owl rotates its head through an angle of 2700 as its eyes do not rotate in their sockets. Each eye is fixed like a car headlight.

31. Copulatory organ (true penis) is present in ostrich, duck, swan and goose.

32. Famous Indian Ornithologist-Dr. Salim Ali.

33. National bird-Pavo cristatus (Peacock).


They are terrestrial, warm-blooded (endothermous) or homeothermal animals so that their body temperature remains constant inspite of the changes in the temperature of the environment.

General characters of this class are :

1. The skin is covered with epidermal hair which acts as an insulating layer and allows high body temperature to be maintained. The hair may be partly lost as a secondary adaptation. In some aquatic mammals where hair is negligible, there is a subcutaneous layer of heat which provides insulation of heat and makes the warmblooded condition possible.

2. The skin has two kinds of glands, sudorific glands which produce sweat -evaporation of sweat controls the body temperature; second kind of glands are sebaceous glands which produce an oily secretion which makes the hair water-resisting. Modified sweat glands (sudoriferous) form mammary glands which produce milk in the females for nourishment of the young for some time after birth. Because they possess mammae (breasts) and mammary glands, they are called mammals. It is the most unique character of mammals.

3. Them is an external ear or pinna with an external auditory meatus. This is in addition to middle and internal ear.

4. In higher mammals, the anus is separated from the urinogenital aperture; consequently urinary and genital ducts have no connection with the digestive tube.

5. In males, testes have come to lie outside the body cavity in scrotal sacs (except in elephants and aquatic mammals and prototherian mammals).

6. Teeth are embedded in sockets of the jaw bone and are said to be thecodont. There are only two sets of teeth in life time, one deciduous or milk set and another permanent set, this condition is spoken of as diphyodont. There are four different types of teeth, hence mammals are heterodont.

7. A muscular diaphragm divides the coelom into a thoracic and an abdominal cavity; the thoracic cavity has a pericardial cavity containing the heart and two pleural cavities containing the lungs, the remaining viscera lies in the abdominal or peritoneal cavity.

8. The heart is 4-chambered with two auricles and two ventricles so that oxygenated blood lies in the left half and deoxygenated blood in the right half. This condition is also found in birds. Only the left aortic arch is present. Erythrocytes are round, biconcave and non-nucleated (except in camel where they are oval and non-nucleated).

9. Cerebral hemispheres and cerebellum are large-sized and highly developed with great increase in the cortex. The two cerebral hemispheres are joined by a transverse band of nerve fibres called corpus callosum. There are four solid optic lobes called corpora quadrigemina in the mid-brain. 12 pairs of cranial nerves.

10. The middle ear has three ear ossicles called malleus, incus and stapes; the internal ear has a spirally coiled cochlea as an efficient organ of hearing.

11. The neck generally has seven cervical vertebrae.

Example : Oviparous-Ornithorhynchus (Platypus); Viviparous -Macropus (Kangaroo), Pteropus (Flying fox), Camelus (Camel), Macaca (Monkey), Rattus (Rat), Canis (Dog), Felis (Cat), Elephas (Elephant), Equus (Horse), Delphinus (Common dolphin), Balaenoptera (Blue whale), Panthera tigris (Tiger), Panthera leo (Lion). etc.

(a) Ornithorhynchus (b) Macropus (c) Pteropus (d) Balaenoptera



Concept Builder

1. How many vertebrae do giraffes have in their neck?

Most of the vertebrates, including giraffes and camel, have seven cervical (neck) vertebrae. At almost 6 m (20 ft) tall, the giraffe is the tallest of all vertebrates and its seven cervical vertebrae are greatly elongated

Exception : 3 toed sloth (Bradypus) with 9 cervical vertebrae and Manatee is with 6 neck vertebrae.

2. Armadillos : The nine-banded armadillo (Dasypus) is one of the few mammalian species whose range is expanding. In late 1800s, they lived only as far north as central Texas. Leprosy bacteria is cultured in the armadillos (Dasypus).

Concept Builder

1. Man remains plantigrade at rest or during locomotion. Uses only the toes for running, thus is called sub plantigrade.

2. Colour of human skin is yellow to orange due to carotene pigment in cells of stratum corneum and subdermal fat cells. Melanin is found in melanocytes.

3. In man sweat glands are absent at lip borders, clitoris, glans penis, nail beds, under surface of prepuce.

4. Sweat or sudoriferous glands secrete sweat. Sweat comprises of 95% water and 5% metabolic waste.

5. Spiny ant eater, scaly ant eaters, moles, cetaceans, sirenians and some edentates do not possess sweat glands.

6. Tusks of elephants are two incisors of upper jaw which constantly grow throughout life.

7. Man

8. Dog

9. Cat

10. Rat

11. Horse

12. Elephant

13. Primates such as monkeys, man, apes, etc., acquired 3 dimensional vision due to their most evolved motor understanding of visual sensation.

14. Deer, amongst vertebrates, proportionately to their body size, possess largest eyes.

15. Carnassial Teeth. Special shearing teeth in carnivores for cracking bones-4th premolar of upper jaw and first molar of lower jaw.

16. Milk Producing Male Mammal. Spiny Ant Eater/Echidna.

17. Monotreme. With a single aperture of cloaca for urinogenital and digestive tracts.

18. Largest Land Animal. Loxodonta africana/African Elephant. Height 3.5 m and weight 7 tonnes.

19. Tallest Land Animal/Mammal. Giraffe, upto 6 m.

20. Mouse and Rat. Mouse and Rat has first molar bigger than combined 2nd and 3rd molars.

21. Zebra Stripes. Stripes of no two zebras are alike.

22. Fastest Mammal. Acinonyx jubatus/(Cheetah) (extinct from India but present in Africa). Speed upto 100 km/hr.

23. Slowest Terrestrial Mammal. 3-toed Sloth/Bradypus, Tridactylus, 100-150 m/hr.

24. Slowest Aquatic Mammal. Sea Otter/ 10 km/hr.

25. Longest Gestation Period in Mammal. 609 days/20 months in Elephas maximus.

26. Shortest Gestation Period in Mammal. Opossum. 12-13 days.

27. Hom. Matted hair in Rhino. Antlers are solid, shed and regrown every year.

28. Tiger. Panthera tigris is National animal of India (declared in 1973).

29. Today Marsupials are found mainly in Australia except a few marsupials such as the American opossum are found outside that continent.

30. Rabbit is digitigrade because it moves on digits.

31. Plantigrade mammals are those whose palm and sole touch the ground when moving from one place to another e.g., bears and certain insectivores.


32. Unguligrade mammals are those whose only the tips of one or two fingers and toes remain in contact with the ground both at rest and locomotion. These are fastest running terrestrial mammals e.g., horses, deers, cows, donkeys etc.

33. Hides are prepared from dermis of animal skin.

34. Seals and whales have scanty hairs because heat insulation is done by blubber.

35. Horns of rhinoceros, scales of scaly ant eater and spines of porcupine are derivatives of hairs.

36. Retina of owls contains only rods (suitable for nocturnal habit). Also, the same occurs in shrews, hedge hog, rodents, bats etc.

37. Retina of fowls contains only cones (suitable for diurnal habit). Squirrels also have only cones.

38. Whales, mice, shrews and also some other mammals, but not rabbit and man, posses Harderian gland like that of frog.

39. Scrotum of mammals contains testes, in most of the mammals; this is a thermostatic chamber for testes and lies outside the abdominal cavity because sperms cannot develop in body temperature. Thus, these become close, if the temperature falls more than 2°C or come apart from the body, if temperature rises more than 2°C.

40. In insectivores, chiroptera and rodentia scrotum is formed only during breeding season, later move to abdominal cavity e.g., bat, otter.

41. Insectivores, edentates, proboscidians (elephants), cetaceans (whales) always have their testes inside the body cavity.


1.    Phylum Chordata includes animals which possess a notochord either throughout or during early embryonic life. Other common features observed in the chordates are the dorsal, hollow nerve cord and paired pharyngeal gill slits. 

2.    Some of the vertebrates do not possess jaws (Agnatha) wheares most of them possess jaws (Gnathostomata). Agnatha is represented by the class Cyclostomata. They are the most primitive chordates and are ectoparasites on fishes. 

3.    Gnathostomata has two super classes. Pisces and Tetrapoda. Classes chondrichthyes and osteichthyes bear fins for locomotion and are grouped under pisces. The chondrichthyes are fishes with cartilaginous endoskeleton and are marine and Osteichthyes class includes bony fishes. 

4.    Classes Amphibia, Reptilia, Aves and Mammalia have two pairs of limbs and are thus grouped under Tetrapoda. The amphibians have adapted to live both on land and water. Reptiles are characterised by the presence of dry and cornified skin. Limbs are absent in snakes. Fishes, amphibians and reptiles are poikilothermous (cold-blooded). Aves are warm-blooded animals with feathers on their bodies and forelimbs modified into wings for flying. Hind limbs are adapted for walking, swimming, perching or clasping. The unique features of mammals are the presence of mammary glands and hairs on the skin. They commonly exhibit viviparity.