SUPERCLASS-TETRAPODA
Tetrapoda is subdivided into four main classes, i.e.,
Amphibia, Reptila, Aves and Mammalia.
These are given below as
1. Class—Amphibia
The class—Amphibia (Amphi—double; bios—life) includes
about 6771 species. These animals are frogs, toads,
salamanders and caecilians. They are the first
cold-blooded vertebrates, which ventured to live on land
from water.
The common features of amphibians are
(i) They live in freshwater and on moist land.
(ii) Body is compressed and cylindrical and
differentiated into head and trunk.
(iii) Nostrils are connected to the buccal cavity eyes
have eyelids. A pair of external nares for olfaction,
a pair of eyes with movable eyelids are present.
Tympanum represents the ear.
(iv) Skin is mostly smooth, moist, highly vascular and
rich in gland. Scales are generally absent. It helps
in cutaneous respiration.
(v) Amphibians mostly have two pairs of pentadactyl
limbs. They are used for locomotion.
(vi) Skeleton is bony. Notochord does not persist. Skull is
dicondylic (i.e., it has two occipital condyles). Most
vertebrae are procoelous.
(vii) Digestive system is well-developed, Mouth is large and
armed with teeth in upper or lower jaw or both the jaws.
Vomarine teeth also found. Amphibians are first
vertebrates in which true tongue is found (a true tongue
contains muscles and is protrusible). Alimentary canal
leads into cloaca.
(viii) Respiration occurs by gills, lungs lining of
buccopharyngeal cavity and skin either separately or in
combination. Gills are always present in the larvae that
may or may not persist in adult stage.
(ix) Heart is three-chambered, with two auricles and one
ventricle. Aortic arches occur in three pairs. RBCs are
oval, biconvex and nucleated.
(x) Kidneys are mesonephric. Amphibians are mostly
ureotelic.
(xi) Larvae and adult aquatic amphibian show lateral line
sensory system.
(xii) Cranial nerves are ten pairs.
(xiii) Fertilisation is usually external, but sometimes internal
as seen in Salamendra and Ichthyophis.
(xiv) Development is indirect and arval stage called tadpole.
(xv) They are oviparous. Adult female lays eggs and the
embryo develops inside the eggs.
(xvi) Amphibians undergo hibernation in winter and
aestivation in summer to avoid extremes of
temperature, e.g., tail less amphibians are Rana (frog),
Bufo (toad), Hyla (tree frog), Rhacophorus (flying frog), etc.
Tailed and limbed amphibians are Salamandra
(salamander), Amblystoma (tiger salamander), limbless
amphibian is Ichthyophis.

2.Class – Reptilia
The class—Rcptilia (Reptare, repere or reptum — to
creep) includes about 9500 species that include
animals like lizards, snakes,
turtles,
tortoises,
crocodiles, etc. Reptiles are the first fully adapted
terrestrial animals.
They dominated the earth about 200 millions year ago
in the Jurassic period of Mesozoic era, called the
golden age of reptiles. During this period many huge
sized reptiles lived on earth, swarm on water and flew in
the air. These fossil reptiles are known as dinosaurs.
The largest reptiles of today are pythons (10m),
crocodiles (7 m) and komodo dragon (3m).
The general features of reptiles are given below
(i) They are terrestrial, a few of them live in water,
such as tortoise, crocodile, etc.
(ii) The body may be long, cylindrical or short and
broad. It is divisible as head, neck, trunk and
tail.
(iii) They have dry, rough and non-glandular skin. It
is provided with horny, epidermal scales or
scutes.
(iv) Appendages are of two pairs of pentadactyl
limbs with powerful horny claws. Limbs are
locomotor-y organs.
(v) Endoskeleton is bony. Skull is monocondylic
for articulation with the vertebral column.
(vi) Digestive system is well-developed. •rhe mouth
is large with acrodont teeth in both the jaws.
Jaw bones are movable to swallow large prey.
(vii) Lungs are respiratory organs. Ribs help expand
and contract body cavity making the lungs
more efficient. Turtles show cloacal respiration.
(viii) Heart is usually three-chambered with two
auricles and one ventricle. The ventricle is
incompletely divided by a septum. The heart is
four-chambered in crocodiles. RBCs are oval,
biconvex and nucleated.
(ix) Excretion occurs through kidneys. The
landforms release uric acid, while aquatic forms
excrete urea.
(x) Nervous system contains 12 pairs of cranial
nerves.
(xi) Sense organs like eyes, ears (tympanum) and
nose are well-developed. But they do not have
external ear openings.
(xii) Reptiles are cold-blooded (poikilothermic)
animals. They hibernate in winter. Snakes and
ligands shed their scales as skin cast.
(xiii) These are unisexual and show sexual dimorphism.
Fertilisation is internal. Most reptiles are oviparous and
some are ovoviviparous, such as vipers, sea snakes, etc.
The eggs are retained inside the body of the mother and growing
embryos derive shelter and nourishment from the mother
Development is direct.
e.g., Calotes (garden lizard), Draco (flying lizard), Chameleon
(arboreal lizard), Hemidactylus (wall lizard),
(crocodile), Alligator (alligator), Sphenodon (tuatara-the living
fossil), Naja (cobra), Bungarus (krait), Vipera (viper).

3.Class-Aves
The class—Aves (avis — bird) or flying vertebrates include about
10052 species. An immense variety in birds is found such
parrots, pigeons, crows, ostrich, penguins, ducks, sparrous
kingfishers, etc.
The general features of class—Aves arc listed below
Note
Birds are well-known for thetr attractive body colours and Interesting
like singing. nest budding. parental care and migration.
(i) Birds have aerial mode of life. They spend most of thc
time in air. (arborrhael) Characteristic feature of
the presence of feathers.
(ii) The body is usually streamlined. It is divided into hed
neck, trunk and tail.
sulatot
(iii) Exoskeleton consists of light feathers. It acts as in
and helps in flight. Most of them fly except the flightle
birds (e.g., ostrich). The skin is dry without glands
the oil gland at the base of the tail.
(iv) Endoskeleton is fillly ossified (i.e., bony) and is
made up of delicate and light bones with air
cavities (pneumatic).
(v) Locomotion occurs through wings. They have
modified forelimbs into wings. Hindlimbs
generally have scales and are modified for
walking, swimming or clasping the tree
branches.
(vi) The digestive system of birds has additional
chambers, the crop and gizzard. Alimentary canal
leads into three-chambered cloaca.
(vii) Lungs are respiratory organs, which are spongy,
inelastic and are connected to large air sacs. The
pharynx is without voice box and voice is
produced by special organs called syrinx present
at the base of trachea.
(viii) Excretory organs are kidneys that are
metanephric in adults. Excretory matter is
mainly uric acid and urine is semisolid.
(ix) Heart is four-chambered with two auricles and
two ventricles. Only right aortic arch persists.
Red Blood Corpuscles (RBCs) are oval,
biconvex and nucleated.
(x) Birds are warm-blooded or homeotherrnal
animals, i.e., they maintain the constant body
temperature.
cranial
(xi) Nervous system contains 12 pairs of cranial
(xii) Sexes are separate with sexual dimorphism. Irft
ovary is present in females, while the right one
is absent. Fertilisation is internal.
(xiii) Birds are oviparous. Eggs possess
extraembryonic membrane and development is
(xiv) Cleidoic eggs are present and are covered by
calcareous shell.
e.g., Flight birds, Corvus (crow), Passer
(sparrow), Columba (pigeon), Psittacula
(parrot), Anas (duck), Pavo (peacock), Milvus
(kite), Neophron (vulture), etc.
Flightless Birds Emu, kiwi, rhea, Struthio
(ostrich), Aptenodytes (penguin), etc.
Knowledge Plus
Largest bird is Struthio camelus (8 feet).
• Smallest bird is Mellisugo helenae (5.5 cm long).
• Largest laying bird is ostrich (1.5 lit.).
• Fastest runner bird is Struthio (ostrich) (30 krwhour).
• Fastest swimmer bird is Pygosce/is papua

4. Class-Mammalia
The class—Mammalia (Mamma – breast) includes about 5499
species. The examples of Mammalia are bats, tigers, lions,
elephants, whale, rat, rabbits, horses, sheeps, monkeys, etc. The
term Mammalia was introduced by Linnaeus in 1758.
The general features of class— Mammalia are as follows
(i) Mammals are found in a variety of habitats, such as
forests, grasslands, mountains, deserts, polar ice caps, caves,
etc. Some of them have adapted to fly or live in water.
(ii) The body is divided into head, neck, trunk and tail.
(iii) The presence of mammary glands is the most
characteristic feature of mammals. Their number varies
from two to many. Mammary glands are well-developed
in females.
(iv) Skin in mammals is unique in possessing hair and is
covered with sweat glands and sebaceous glands.
(v) Exoskeleton contains feathers, hairs, fur, nails, claws,
horns, hooves, etc. External ear called pinnae are present.
They are the skin derivatives.
(vi) Endoskeleton possesses skull and vertebrae. Vertebrae are
connected by intervertebral discs.
(vii) Two pairs of pentadactyl limbs are present for walking,
running, climbing, burrowing, flying and swimming.
Forelimbs are modified as flippers in whales. The digits
end with horny nails, claws or hoofs.
(viii) Digestive system comprises of complete digestive system.
Different types of teeth are present in the jaw.
(ix) Lungs are spongy and elastic. A sound producing organ
called larynx is also present in mammals.
(x) Heart is four-chambered with two auricles and two
ventricles. RBCs are oval, biconcave and enucleated.
(xi) Excretory organs are kidneys. They excrete urea.
(xii) Brain is well-developed with large convoluted cerebrum and
cerebellum. 12 pairs of cranial nerves are present.
(xiii) Sense organs are well-developed. Ear comprises of three
regions i.e., internal, middle and external. External
opening is protected by a large fleshy pinna. Eyes are
protected by lids of which upper one is movable.
(xiv) Mammals are unisexual and show prominent sexual
dimorphism. Gonads are paired. The testes present
in males descend into scrotal sacs. Most of them are
viviparous except prototherians.
(xv) Fertilisation is internal. Embryo develops in the
uterus. The foetus is connected to uterine wall
through placenta and gets nutrition and respiration.
Placenta formation is not found in prototherians.
(xvi) Development is direct. Larval stage is not present.
They are amniotes, i.e., the embryo develops four
embryonic layers during development.

(xvii) They are viviparous generally. Exeption is
Ornithorhynchus (platypus), which is oviparous.
Parental care is highly developed. ‘I’hey feed their
young ones on their milk and protect them from
enctnies, e.g.,
ltfacropus (kangaroo), Pteropus (flying fox), Cameluj
(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).

CLASSIFICATION OF
PHYLUM-CHORDATA
The classification of phylum—Chordata
is divided into three subphyla, i.e.,
Urochordata(Tunicata),
Cephalochordata and Vertebrata.
Subphyla—Urochordata and
Cephalochordata are often referred to
as protochordates and are exclusively
marine.
Details of each subphyla and its
numerous classes are given below
SUBPHYLUM-UROCHORDATA
The body is covered by a testa (tunic) composed largely of
tunicine. So, they are commonly called as tunicates. The
notochord is present only in the tail of the larva and
disappears in the adult. Coelom is absent, digestive tract is
complete, respiratory system has two to numerous gill slits in
the pharyngeal wall. Circulatory system is open and has
simple tubular heart. Larva undergoes retrogressive
metamorphosis, e.g., Ascidia, Herdmania (sea squirt), Salpa,
Doliolum.
SUBPHYLUM- CEPHALOCHORDATA
In cephalochordates, the notochord extends the entire length
of the body and passes a head of the nerve cord in front’
Notochord persists throughout the life. A true enterocoelous
coelom is present. It is, however reduced in the pharyngeal
region of atrium, e.g., Branchiostoma (amphioxus).
SUBPHYLUM-VERTEBRATA
The subphylum—Vertebrata represents advanced or higher
chordates which include vertebrates or craniates. Notochord
is present only in the embryonic stage. In adults, it is replaced
by a vertebral column consisting of ring-like bones called
vertebrae.
The anterior part of the notochord is however, replaced by
skull or cranium to protect brain, hence named Craniata
Pharyngeal gill slits persist only in adults of lower forms.
Circulatory system is closed type with ventrally situated heart
and hepatic portal system. Respiratory pigment haemoglobin
of  is present in blood corpuscles. Excretory organs consist
of a pair of kidneys. They are unisexual and lack
reproduction.