CHORDATA | NEET UG

CHORDATA

Created by: B Mokshagna Reddy (BMR)

Introduction to Phylum - chordata

❖Chordates are animals characterized by the presence of notochord at some stage during their development. Members possess a hollow nerve cord and pharyngeal gill slits.

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The other general characteristic features of Chordates are as follows
❖They are bilaterally symmetrical, triploblastic, and coelomate with the organ-system level oforganization.
❖They hold a post-anal tail.
❖The body includes a closed circulatory system.
❖In some members of Phylum Chordata, the notochord is present only in the larval tail, and in some, it is present throughout their life from head to tail region.
❖Chordates have many sub-divisions and Protochordates are one of the earliest to evolve.

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❖Three subphylums come under Chordata:
1. Urochordata– notochord present only in the larval tail, e.g. Ascidia, Salpa, Doliolum
2. Cephalochordata– notochord present throughout life from head to tail,
Ex : Branchiostoma (Lancelet or amphioxus)
3. Vertebrata–Notochord is present in the embryonic stage, it gets replaced by Vertebral Column

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❖Vertebrata is further divided into two divisions.
1. Agnatha (without jaws): Class Cyclostomata
2. Gnathostomata (with jaws): has two Super Class:
A. Pisces (bear fins): two Classes- Chondrichthyes, Osteichthyes
B. Tetrapoda (bear limbs): four classes- Amphibia, Reptilia, Aves and mammals

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Sub Phylum – Urochordata

❖It is also referred to as Tunicata which are marine animals.
❖The body of these animals is surrounded by a leathery covering (similar to a tunic, hence the name).
❖ Larvae are free-swimming, the notochord is present only in the tail of larvae and after settling on the seabed, they get transformed into sessile adults.
❖They are generally hermaphrodites.
Ex : Ascidians, Doliolum, Oikopleura, etc.
➢Sub Phylum – Cephalochordata :
❖It mainly consists of small, fish-like marine animals in which the notochord is extended along the entire body.
❖The animals also have pharynx, which is large with numerous gill- slits.
❖Members of this subphylum have separate sexes.
Ex : Amphioxus or lancelet Ascidia

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Sub Phylum Vertebrata

❖Presence of a true vertebral column and internal skeleton with muscle attachment points for body movement.
❖A front-side muscular heart with two, three or four chambers.
❖Kidneys for excretion and osmoregulation
❖A paired appendages which may be fins or limbs.
❖Possess notochord during the embryonic stage.
❖Vertebrates are the only chordates to possess a brain as a part of the central nervous system.

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Classification of Vertebrates

1. Cyclostomes
2. Pisces : Chondricthyes and Osteichtyes
3. Tetrapoda : Amphibia, Reptilia, Aves and Mammals

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Classification of Sub Phylum Vertebrata

▪ Agnatha and Gnathostomata are divisions of Sub Phylum vertebrata.
▪ Pisces and Tetrapoda are super class of division Gnathostomata.
▪ Pisces include Classes Chondricthyes and Osteichthyes.
▪ Tetrapoda includes Classes Amphibia, Reptilia, Aves and mammalia.
▪ Reptilia, Aves and mammalia are amniotes due to Internal fertilization.
▪ Chondricthyes, Amphibians, Reptiles and Birds have cloaca.
▪ A total of 8 classes are present in sub phylum Vertebra I.e., Cyclostomes, Chondricthyes, Osteichthyes, Amphibia, Reptilia, Aves and Mammals.

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Division Agnatha

❖ Animals are without jaws and contains only one class Cyclostomes.
• 1. Cyclostomata (Circular Mouthed Fishes) :
▪ Characterised by circular and sucking mouth without jaws
▪ Ectoparasites on fishes
▪ 6-15 pairs of gill slits
▪ Scales and fins are absent
▪ Cartilaginous vertebral column and cranium
▪ Closed type circulation
▪ Marine but migrate to freshwater for spawning where they die, larvae after metamorphosis come
• back to the ocean.
• Ex : Petromyzon (Lamprey), Myxine (Hagfish)

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Division Gnathostomata

❖Animals with jaws.
❖This division consists of 2 super classes Pisces and Tetrapods.

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1. Chondricthyes (Cartilaginous fishes)

▪ Cartilaginous endoskeleton, the mouth is on the ventral side
▪ Gill is without operculum
▪ The notochord is present throughout life
▪ Placoid scales are present on the skin which makes it tough
▪ It swims constantly to avoid sinking as air bladders are absent
▪ Two chambered heart and poikilothermous (cold-blooded)
▪ Separate sexes, internal fertilisation and many are viviparous
▪ Claspers are present on male’s pelvic fin
▪ Electric organs are present in Torpedo and Trygon has poison sting
• Ex : Scoliodon (Dogfish), Trygon (Stingray), Pristis (Sawfish), Carcharodon (Great white shark)

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2. Osteichthyes (Bony fishes)

▪ Streamlined body, bony endoskeleton, 4 pairs of gills with operculum
▪ Skin is covered by cycloid scales
▪ Two chambered heart and air bladder for buoyancy, poikilothermous
▪ Sexes are separate, oviparous, external fertilisation with direct development
Ex : Marine- Hippocampus (Sea horse), Exocoetus (Flying fish)
Freshwater- Labeo (Rohu), Clarias (Magur), Catla (Katla)
Aquarium- Betta (Fighting Fish), Pterophyllum (Angelfish)

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Super class Tetrapoda

❖Tetraods bear limbs.
❖This super class contains classes Amphibia, Reptilia, Aves and Mammalia.

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Super Class Pisces (Fishes)

❖ They are aquatic animals, having a streamlined body and a pair of fins which are used for propulsion and movement.
❖ Furthermore, fish are cold-blooded, but the discovery of a new species in 2015 has changed this perception.
❖ The opah or the moon-fish is a fully warm-blooded fish capable of regulating its body temperature.
❖ Endoskeleton may be cartilaginous or bony and respiration occurs through gills.
❖ They do not possess eyelids because the surface of the eye is to be kept moist all the time.
Ex : Dogfish and Rohu.
❖ The super class pisces is divided into Classes Chondricthyes and Osteichthyes.

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1. Class Amphibia

▪ These can live both on land and in water.
▪ They are ectothermic animals, found in a warm environment.
▪ Their body is divided into head and trunk. The tail may or may not be present.
▪ The skin is smooth and rough without any scales, but with glands that make it moist.
▪ They have no paired fins. Unpaired fins might be present.
▪ They have two pairs of limbs for locomotion.
▪ They respire through the lungs and skin. Gills might be present externally in some adults.
▪ The heart isthree chambered.
▪ The kidneys are mesonephric. The excretory material includes ammonia and urea.
▪ They possess ten pairs of cranial nerves.
▪ The lateral line is present during their development.
▪ The sexes are separate and fertilization is usually external. However, in salamanders, the fertilization is internal.
▪ Development is indirect with metamorphosis.
▪ Breeding occurs in water. The copulatory organs are absent in males.
Ex : Bufo (Toad), Rana (Frog), Hyla (Tree frog), Salamandra (Salamander), Icthyophis (Limbless amphibia)

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2. Reptilia

▪ These are creeping and burrowing terrestrial animals with scales on their body.
▪ They are cold-blooded animals found in most of the warmer regions of the world.
▪ Their skin is dry, and rough, without any glands.
▪ The body is divided into head, neck, trunk, and tail.
▪ Few of these shed the scales on their skin as skin cast.
▪ The respiration takes place with the help of the lungs.
▪ The skull is monocondylic.
▪ Limbs may or may not be present. If they have limbs, they are two pairs of pentadactyl limbs,each bearing claws. Snakes do not have limbs.
▪ The heart is 3 chambered. However, crocodiles have a 4-chambered heart.
▪ The nervous system comprises 12 pairs of cranial nerves.
▪ Reptiles do not have external ear openings. Tympanum represents ear
▪ They possess a typical cloaca.
▪ Reptiles are generally uricotelic. They mostly excrete nitrogenous wastes as uric acid.
▪ Fertilisation is internal.
▪ They are oviparous and the eggs are very yolky. Development is direct.
Ex : 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).

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3. Aves :

▪ Birds are warm-blooded animals.
▪ Their forelimbs are modified into wings.
▪ They have well-developed flight muscles that help during the flight.
▪ Their hind limbs are adapted for walking, hopping, perching, grasping, wading and swimming.
▪ There are epidermal scales on their legs.
▪ The endoskeleton is bony with long hollow bones filled with air cavities. known as pneumatic bones.
▪ Their spindle-shaped body minimizes resistance of the wind.
▪ The feathers help in preventing heat loss and reduce air friction by providing passage to the air.
▪ There is no skin gland except the oil gland.
▪ The lower and upper and jaws are modified into a beak.
▪ They have no teeth.
▪ They have sharp eyesight.
▪ The alimentary canal has a crop and a gizzard. The crops help in softening food, and the gizzard helps in crushing the food.
▪ Pigeons and other seed-eating birds lack a gall bladder.
▪ They have spongy and elastic lungs for respiration.
▪ The special vocal organ called syrinx is present at the base of trachea.
▪ Their heart is four-chambered.
▪ RBCs are oval, nucleated and biconvex.
▪ 12 pairs of cranial nerves are present.
▪ They have a single ovary and oviduct on the left side
▪ All the birds are oviparous and exhibit sexual dimorphism. The eggs have four embryonic membranes- amnion, chorion, allantois, and yolk sac.
Ex : Corvus (Crow), Columba (Pigeon), Psittacula (Parrot), Struthio (Ostrich), Pavo (Peacock), Aptenodytes (Penguin), Neophron (Vulture)

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4. Mammalia :

▪ Mammals are warm-blooded animals who give birth to their younger ones.
▪ They are the most dominant form of animals found in almost all types of habitats.
▪ They have mammary glands that help them produce milk to feed their younger ones
▪ Presence of region of the brain known as Neocortex
▪ Their skin possesses oil glands (sebaceous glands) and sweat glands (sudoriferous glands).
▪ The fur of hair throughout the body which helps animals adapt to their environment.
▪ They are heterodont, i.e., possess different types of teeth.
▪ Mammals also possess cervical vertebrae.
▪ The skull is dicondylic.
▪ The trunk is divided into thorax and abdomen.
▪ The mammals respire through lungs.
▪ Good sense of hearing as mammals are aided with 3 middle ear bones
▪ Mammals have a four-chambered heart. The sinus venous and renal portal system are absent.
▪ Presence of single-boned lower jaws.
▪ The brain is well developed divided into cerebrum, cerebellum and medulla.
▪ They possess 12 pairs of cranial nerves.
▪ Exhibit one of the most advanced forms of Diaphragms.
▪ The mammals can lay eggs also. They are known as viviparous.
Ex : 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).

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