All chordates possess three fundamental distinct features at some stage of their life cycle, they are:
1.Presence of elongated rod like notochord below the nerve cord and above the alimentary canal. It serves as primate internal skeleton. it may persist throughout life in lancelets and lampreys. In adult vertebrates, it may be partially or completely replaced by backbone or vertebral column.
2. A dorsal hollow or tubular fluid filled nerve cord lies above the notochord and below the dorsal body wall. It serves to integrate and co-ordinate the body functions. In higher chordates, the anterior end of the nerve cord gets enlarged to form the brain and the posterior part becomes the spinal cord, protected inside the vertebral column.
3. Presence of pharyngeal gill slits or clefts in all chordates at some stage of their lifecycle. It is a series of gill slits or clefts that perforates the walls of pharynx and appears during the development of every chordate. In aquatic forms, pharyngeal gill slits are vascular, lamellar and form the gills for respiration. In terrestrial chordates, traces of non- functional gill clefts appear during embryonic developmental stages and disappear later. Besides the above said features, chordates are bilaterally symmetrical. 

(i) Amphibians are the first vertebrates and tetrapods to live both in aquatic as well as terrestrial habitats.
(ii) They are poikilothermic.
(iii) Their body is divisible into the head and trunk and most of them have two pairs of limbs; tail may or may not be present.
(iv) Their skin is smooth or rough, moist, pigmented and glandular.
(v) Eyes have eyelids and the tympanum represents the ear.
(vi) Respiration is by gills, lungs and through the skin.
(vii) Heart is three chambered.
(viii) Kidneys are mesonephric. Sexes are separate and fertilization is external.
(ix) They are oviparous and development is indirect. They show hibernation and aestivation.
(x) eg. Bufo (Toad), Rana (Frog).

(i) This is the second largest animal phylum.
(ii) Molluscs are terrestrial or aquatic (marine or fresh water) and exhibit organ system level of body organisation.
(iii) They are bilaterally symmetrical (except univalves), triploblastic and coelomate animals.
(iv) Body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot and a visceral hump or visceral mass.
(v) A soft layer of skin forms a mantle over the visceral hump. The space between the visceral mass and mantle (pallium) is called the mantle cavity.
(vi) A number of feather like gills (ctenidia) are present, which are respiratory in function.
(vii) The digestive system is complete and mouth contains a rasping organ called radula with transverse rows of chitinous teeth for feeding (radula is absent in bivalves).
(viii) The sense organs are tentacles, eyes and ospharidium (to test the purity of water and present in bivalves and gastropods).
(ix) Excretory organs are nephridia.
(x) Open type of circulatory system is seen except for cephalopods such as squids, cuttle fishes and octopuses. Blood contains haemocyanin, a copper containing respiratory pigment.
(xi) Development is indirect with a veliger larva.
(xii) eg. Pila (Apple snail).

1. Aves are commonly known as birds. The characteristic feature of Aves is the presence of feathers and the ability to fly except for flightless birds (Eg: Ostrich, Kiwi, Penguin). The forelimbs are modified into wings, and the hind limbs are adapted for walking, running, swimming and perching.
2. The skin is dry and devoid of glands except the oil gland or preen gland at the base of the tail
3. The exoskeleton consists of epidermal feathers, scales, claws on legs and the horny covering on the beak.
4. The endoskeleton is fully ossified (bony) and the long bones are hollow with air cavities (pneumatic bones).
5. The pectoral muscles of flight (pectoralis major and pectoralis minor) are well developed.
6. Respiration is by compact, elastic, spongy lungs that are continuous with air sacs to supplement respiration.
7. The heart is four chambered.
8. Aves are homeothermic. Migration and parental care is well marked. Urinary bladder is absent.
9. Sexes are separate with well-marked sexual dimorphism. In males, the testes are paired but in females, only the left ovary is,well developed while the right ovary is atrophied.
10. All birds are oviparous. Eggs are megalecithal and, cleidoic. Fertilization is internal.
Eg: Corvus (Crow), Columba (Pigeon).

Salient features of Mammals:
1. They are found in a variety of habitats. Their body is covered by hair, a unique feature of mammals.Some of them are adapted to fly or live in water.
2. Presence of mammary glands is the most unique feature of mammals 
3. They have two pairs of limbs adapted for walking, running, climbing, burrowing, swimming and flying 
4. Their skin is glandular in nature, consisting of sweat glands, scent glands, and sebaceous glands. Exoskeleton includes horny epidermal horns, spines, scales, claws, nails, hooves and bony dermal plates
5. Teeth are thecodont, heterodont and diphyodont. External ears or pinnae are present. The heart is four chambered and possess a left systematic arch.
6. Mature RBCs are circular, biconcave and non nucleated. Mammals have a large brain when compared to other animals. They show the greatest intelligence among all animals.
7. Their kidneys are metanephric and are ureotelic. All are homeothermic, sexes are separate and fertilization is internal.
8. Eg: Oviparous- Ornithorhynchus (Platypus), Viviparous- Macropus (Kangaroo).