Phylum-Chordata 

Chordata is a phylum of triploblastic bilaterally symmetrical coelomate animals.

Notochord is a long rod-like structure that develops between the dorsal nervous system and gut. Notochord functions as a support structure that provides points for attachment to muscles. Dorsal hollow nerve cord occurs above the notochord. 

Pharyngeal gill slits (gill pouches) are paired respiratory structures which remain functional throughout life in fishes and some amphibians. In others they occur only in embryos.

Post anal tail occurs in most chordates for balancing, protection of genital and anal regions.

Phylum chordata is divided into three subphylum -

(i) Urochordata (e.g. Herdmania)

(ii) Cephalochordata (e.g. Amphioxus)

(iii) Vertebrata

Subphylums Urochordata and Cephalochordata are often referred to as protochordata. 

Notochord is present only in the tail of free living tadpoles like larva in urochordata. 

Notochord, Nerve cord and pharyngeal gill clefts remain throughout the life span in cephalochordata.

1.0Protochordata

These animals are bilaterally symmetrical, triploblastic and have a coelom. Notochord is present at least at some stages during their lives. It provides a place for muscles to attach for ease of movement.  Protochordates may not have a proper notochord present at all stages in their lives or for the entire length of the animal. 

Protochordates are marine animals. 

2.0Vertebrata

Vertebrates are bilaterally symmetrical, triploblastic, coelomic and segmented animals. In vertebrates, the notochord is replaced by a true vertebral column. The nerve cord remains enclosed within the vertebral column. Vertebrata are grouped into six classes:-

(i) Cyclostomata (ii) Pisces (iii) Amphibia

(iv) Reptilia (v) Aves (vi) Mammalia

Cyclostomata

Cyclostomes are jawless vertebrates. They are characterised by having an elongated eel-like body, circular mouth, slimy skin and are scaleless. They are ectoparasites or borers of other vertebrates. 

e.g. Petromyzon (Lamprey) and Myxine (Hagfish).

 Pisces

True fishes are included in this class. They respire through gills. They are exclusively water living animals. Their body is streamlined and covered by scales/plates. They have muscular tails and paired fins for movement. Their endoskeleton is made up of either cartilage or bones or both. 

They are unisexual and lay eggs. They are cold blooded. The heart is two chambered.

Fishes are of two types based on the nature of their endoskeleton.

1. Cartilaginous fishes

2. Bony fishes

Cartilaginous Fishes

e.g. Scoliodon – Dog fish, Trygon – Sting ray, Torpedo – Electric ray, Rhineodon – Whale shark, Chimaera – ghost shark.

Bony Fishes

e.g. Labeo rohita – Rohu or Indian carp, Anabas – Climbing perch, Caulophyryne jordani - Angler fish, Hippocampus – Sea horse, Pterois volitans - Lion fish, Exocoetus – Flying fish, Synchiropus splendidus - Mandarin fish

Fishes obtain oxygen dissolved in water by using gills.  They are cold-blooded and their hearts have only two chambers, unlike the four that humans have. Skeletons are either made entirely of cartilage, such as sharks, or made of both bone and cartilage, such as tuna or rohu.

 Amphibia

Their skin is smooth or rough, moist, slimy, glandular and without scales. To moist the skin numerous mucus glands are found and skin contains pigment cells (chromatophores) for colouration. The three chambered heart has two auricles and one ventricle. Respiration takes place by gills, lungs, skin and buccal lining. They are cold-blooded animals. They lay eggs. Fertilization is external.

Amphibians are the first vertebrates which come out of water but these are not able to live on land permanently. These depend on water for their reproduction. Two pairs of pentadactyl (five digits) limbs are present. Digits without claws. Excrete either ammonia (by tadpole) or urea (by adults).

The frog is active during the day whereas the toad is active at night. The skin of a frog is moist whereas the skin of a toad is dry and rough. Frog has webbed feet whereas in toads the web is absent.

e.g. Ichthyophis - Blindworm, Salamander, Bufo - Common toad, Hyla - Tree-frog, Rana tigrina - Indian bull frog.

Reptilia 

Skin is dry, cornified, rough and non-glandular. The exoskeleton is made up of horny epidermal scales or dermal scute or bony plates. Heart is three chambered i. e. two auricles and an incompletely divided ventricle. Only crocodiles have four chambered hearts. Fertilization is internal. They breathe through their lungs. These are mostly oviparous, eggs are cleidoic i.e. eggs are covered by a shell made up of calcium carbonate. These are cold blooded animals.

Reptiles are the first successful terrestrial animals but some are aquatic. The body is divided into head, neck, trunk and tail. Two pairs of pentadactyl limbs with incurved nails or claws and one pair of metanephric kidneys are present. They are uricotelic. (i.e. their main excretory waste is uric acid).

e.g. Chelone-marine turtles, Hemidactylus-Common lizard, wall lizard, Python-Azgar (largest snake), Naja-Indian Cobra, Ophiophagus Hannah-King cobra, Vipera-Viper snake, Crocodilus-Crocodile (Muggar).

Differences Between Amphibia and Reptilia

Aves

All types of birds are included in this class. The body is boat shaped and covered with soft feathers, called “plumage”. Fore limbs modified into wings for flight.

Hind-limbs bear four clawed digits and are adapted for walking and perching. Parental care is present. Four chambered hearts with two auricles and two ventricles are present. They excrete uric acid. They breathe through their lungs. Fertilization internal. They are oviparous and lay large eggs, having hard shells. They are warm-blooded animals.

e.g. Gallus - Chicken, Passer - House sparrow, Corvus - Crow, Columba - Pigeon, Psittacula - Parrot, Pavo - Peacock

In birds teeth are absent, jaws form a horny beak. The endoskeleton is made up of hollow, air-filled bones, known as pneumatic bone. A sound producing organ in birds is called syrinx.

Penguins, Emu, Ostrich and Kiwi are flightless birds.

Note:- Ornithology: Study of birds. Salim Ali was a famous ornithologist. He was known as the “Bird man of India”.

Mammalia 

Members are cosmopolitan. The body is divided into head, neck, trunk and tail with movable eyelids. Mammary glands are found in females for baby feeding. The body is covered by a coat of hairs (made of keratin). Cutaneous glands such as sweat glands and oil glands are present. 

The heart is four chambered. Non-nucleated red blood corpuscles are present in blood. Mammals are warm-blooded animals. Sexes are separate, internal fertilization is present, mostly viviparous but a few are oviparous and lay eggs (e.g. Platypus & Echidna), and some like Kangaroos give birth to very poorly developed young ones.

e.g. Macropus – Kangaroo, Pteropus – Flying fox or Bat, Ratus ratus – Rat, Balaenoptera - Blue whale, Canis – Dog, Felis – Cat, Homo sapiens – Man.

Mammals have two pairs of pentadactyl limbs. Fleshy external ear (pinnae) present. Respiration is by one pair of lungs. A horizontal diaphragm is present in between the thorax and abdomen. They excrete urea i.e. ureotelic.