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Phylum Chordata

Evolutionary Tree Diagram Illustrating the Classification of Kingdom Animalia

 

Chordates exhibit the following three fundamental characteristic features:
 

Characteristics

Porifera

Coelenterata

Platyhelminthes

Aschelminthes

Symmetry

Asymmetrical.

Radial.

Bilateral.

Bilateral.

Level of
organization

Cellular level.

Tissue level.

Organ level.

Organ system.

Coelom

No.

No.

Acoelomate.

Pseudocoelomate.

Germ layers

Diploblastic.

Diploblastic.

Triploblastic.

Triploblastic.

Segmentation

No.

No.

No. But presence of proglottids.

No.

Body

Possess endoskeleton made of spicules and spongin.

Outer epidermis and inner gastrodermis with middle
mesoglea.

Soft, dorsoventrally flattened enclosed by single layers.

Presence of cuticle. High fluid pressure in the pseudocoelom maintains body shape (hydroskeleton).

Gut opening

No. Filter feeders.

Coelenteron with a single aperture, mouth. Hence, incomplete digestive system.

Incomplete digestive system.

Complete digestive system with one mouth and one anus.

Respiration

Diffusion.

Through body surface by diffusion.

Through body surface by diffusion.

Through body surface by diffusion.

Circulatory
system

Diffusion by wandering amoeboid cells.

Gastrovascular cavity.

Undeveloped.

Undeveloped.

Excretory system

Through body surface by diffusion.

Through body surface by diffusion.

Through flame cells (protonephridia).

Gland cells. 
Excretory product is ammonia.

Nervous system

No.

Nerve net.

Ladder-like with two main longitudinal nerves.

Consists of circumpharyngeal rings. Sense organs are present.

Reproductive system

Asexually by gemmule formation. Sexually by formation of gametes.

Asexually by budding (polyp). Sexually by gametes (medusa).

Sexes mostly united. Asexually by regeneration.

Exhibits sexual dimorphism.

Unique features

Body wall (outer pinacoderm and inner choanoderm) encloses spongocoel. Water enters through ostia and finally leaves through osculum. All the cavities in a sponge body are intercommunicating and are collectively called water canal system.

Exhibits polymorphism (polyp and medusa).

Presence of cnidoblast or nematocyst or stinging cells on the tentacles for defence and offence.

Great power of regeneration.

No locomotory structures but possess hooks and suckers. Endoparasites.

Round worms. Endoparasites. Development of egg is direct.

Fertilisation is
internal.

No asexual reproduction. Non-muscular intestine.

Examples

Spongia (Euspongia),Spongilla, Euplectella,Hyalonema.

Hydra, Obelia, Physalia, Aurelia.

Planaria, Fasciola
hepatica, Taenia solium.

Ascaris lumbricoides, Ancylostoma, Wuchereria bancrofti.

 

Characteristics

Annelida

Arthropoda

Mollusca

Echinodermata

Symmetry

Bilateral.

Bilateral.

Bilateral.

Radial.

Level of
organization

Organ system.

Organ system.

Organ level.

Organ level.

Coelom

Coelomate.

Coelomate.

Coelomate.

Coelomate.

Germ layers

Triploblastic.

Triploblastic.

Triploblastic.

Triploblastic.

Segmentation

Yes.

Metameres.

Yes.

Also exhibits
cephalization.

No.

No.

Body

Thin cuticle. Single-layered epithelium.

Hydroskeleton.

Exoskeleton is made up of chitin.

Presence of joint appendages.

Soft bodied animals with shell/mantle (proteinaceous/
calcareous).

Represented by a central disc covered by ossicles with spines called pedicillaria.

May bear arms.

Gut opening

Complete.

Gut has both circular and longitudinal muscles.

Complete. Presence of gizzard.

Presence of mouth parts.

Complete.

Complete.

Respiration

Through skin by
diffusion.

Trachea in grass hopper.

Book lungs in spider.

Has gaseous exchange organs called ctenidial gills.

Tube feet for both locomotion and
respiration.

Circulatory
system

Closed circulatory system.

Blood is red
(haemoglobin).

Open circulatory system.

Haemolymph is the circulatory fluid.

Open circulatory system with a heart and an aorta.

Open circulatory system.

Excretory system

Metanephridia.

Malpighian tubule.

Metanephridia.

No.

Nervous system

Circumventric nerve ring and nerve cord with ganglia.

Sense organs are present.

Includes brain and ganglia.

Nervous system consists of nerve ring, visceral nerve cord and pedal nerve cord.

Has central nerve ring with radiating nerves.

Reproductive system

Sexes may be separate or united.

Sexual reproduction.

Sexual.

Usually internal
fertilization.

Sexual.

Sexes are separate.

Unique features

Exhibits metameric segmentation.

Nephridia are also used for osmoregulation.

Closed circulatory system with large blood vessel acting as heart.

Setae in the body wall in most forms.

The largest of all animal phyla and accounts for over three quarter of all currently known living organisms.

Locomotor structure is a muscular foot.

Presence of radula—a belt-like chitinous sheath bearing recurved teeth.

Presence of water vascular system/ambulacral system.

Shows very high power of
regeneration.

Examples

Hirudinaria, leech, Nereis, Pheretima,earthworm.

Insects, crabs (crustaceans), spiders (arachnids), millipede (myriapods).

Snails, oysters, 
octopus.

Sea star, sea
cucumber.

 

  • Presence of a solid supporting structure on the dorsal side of the body called notochord.
  • Presence of a dorsal, tubular nerve cord.
  • Presence of openings in the pharynx called gill slits, at least in the embryonic stages.
  • Phylum chordata includes four subphyla, namely Hemichordata (e.g. Balanoglossus), Urochordata (e.g. Ascidia), Cephalochordata (e.g. Amphioxus) and Vertebrata.

Tree diagram illustrating the classification of phylum Chordata is shown in Figure.

Subphylum Vertebrata

Animals with backbone are called vertebrates. Notochord modified as vertebral column. Vertebrates represent a major group among the advanced animals called chordates.
 


 

Vertebrata is grouped into two superclasses, namely Pisces and Tetrapoda. Superclass Pisces is divided into Chondrichthyes and Osteichthyes. Class Tetrapoda is further classified into Amphibia, Reptilia, Aves and Mammalia.


Superclass: Pisces
Shows the characteristics of the two classes of Pisces, namely Chondrichthyes and Osteichthyes


Shows the key characteristics that distinguishes the four classes of superclass Tetrapoda.

 

Characteristics

Class

Chondrichthyes

Osteichthyes

Defining traits

Paired traits.

Cartilaginous skeleton.

Ventral mouth.

Asymmetrical caudal fin.

Paired fins.

Bony skeleton.

Anterior mouth.

Symmetrical.

Symmetry

Bilateral.

Bilateral.

Coelom

Coelomate.

Coelomate.

Body temperature

Ectothermal.

Ectothermal.

Digestive system

J-shaped stomach.

Spiral valve in intestine.

J-shaped stomach.

Respiratory system

Through gills (5 to 7 gill clefts).

Through gills (seven pairs of gill slits).

Through lungs (swim bladder) in lung fish.

Circulatory system

Two-chambered heart.

Arteries and veins.

Aortic arches in gills.

Two-chambered heart.

Arteries and veins.

Aortic arches in gills.

Excretory system

Kidneys.

Renal gland.

Kidneys.

Integumentary system

Placcoid scales.

Dermal scales.

Ganoid, ctenoid, cycloid scales.

Nervous system

Brain with two hemispheres

Specialised lobes for sight, smell, taste and hearing.

Lateral line system.

Brain with two hemispheres.

Specialised lobes for sight, smell, taste and hearing.

Lateral line system.

Larger optic lobes.

Reproductive system

Separate sexes.

Internal fertilisation.

Oviparous (egg-laying), viviparous (producing living young), ovoviviparous (eggs develop internally).

Separate sexes.

Some external and some internal
fertilisation.

Viviparous and oviparous.

 

Characteristics of Amphibia, Reptilia, Aves and Mammalia

 

Characteristics

Class

Amphibia

Reptilia

Aves

Mammalia

Body form

Varies

May be long and narrow or short and broad.

Divisible into head, neck, trunk and tail.

Divisible into head, neck, trunk and tail.

Boat shaped and streamlined.

It is divisible into head, neck, trunk and tail.

Variously shaped and divisible into head, neck, trunk and tail.

Appendages

Two pairs of pentadactyl limbs each with four to five or fewer digits.

Hind limbs are larger than fore limbs.

Digits are without claws and often have webs.

Two pairs of pentadactyl limbs with five digits bearing horny claws.

Limbs are absent in few lizards and all snakes.

Two pairs of limbs. Fore limbs modified into wings for flight.

Hind limbs alone support the body and are used for perching, walking, hopping and swimming.

Two pairs of pentadactyl limbs adapted for walking, running, climbing.

Each foot bears five or fewer toes provided with horny claws, nails or hoofs.

Skin

Smooth moist skin rich in mucous and poison glands.

Scales are mostly absent.

Rough and dry without glands.

An exoskeleton of horny epidermal scales is always present.

Scales contain keratin (checks loss of water) enabling reptiles to live on dry land.

Thin and dry except for preen or oil gland on tail.

Presence of feathers as exoskeleton.

Feet bear horny dermal scales.

Glandular and covered by epidermal exoskeleton of hair.

Skin glands include sweat glands, oil glands, modified sweat glands (mammary glands).

Endoskeleton

Bony.

Bony.

Has bones but are delicate and light (pneumatic).

Sternum is usually large and with a median keel for attachment of flight muscles.

Bony.

Neck contains 7
cervical vertebrae.

Digestive
system

Mouth is large with teeth (acrodont).

Vomerine teeth may also occur.

Tongue is protrusible.

Alimentary canal leads to cloaca.

Mouth is large armed with teeth on both the jaws.

Tongue may be protrusible or not.

Alimentary canal leads to the cloaca.

Mouth has a wide gape.

Jaws are covered with horny sheath to form strong beaks.

Alimentary canal has crop (stores and softens food) and gizzard (crush and churn the soften food).

Alimentary canal leads into a cloaca.

Mouth is small with movable lips.

Buccal cavity has salivary glands.

Alimentary canal opens out by anus.

Cloaca in most cases is absent.

Respiratory system

Through gills (larval or aquatic stage), lungs, lining of buccopharyngeal cavity and skin.

Through lungs.

Through lungs (spongy and inelastic).

Voice box lies at the division of trachea into bronchi called syrinx.

The larynx does not act as a sound box.

Through lungs (spongy and elastic).

They are enclosed by pleural membrane.

Ribs and diaphragm play a role in breathing.

Circulatory system

Three-chambered heart with two auricles and one ventricle.

Venous heart (supplying mixed blood).

RBCs are oval, biconvex and nucleated.

Four-chambered heart with two auricles and partly divided ventricle.

Crocodiles have a completely four-chambered heart.

RBCs are oval, biconvex and nucleated.

Four-chambered heart.

Heart is relatively large and fast beating for quick supply of adequate amount of blood during flight.

RBCs are oval, biconvex and nucleated.

Four-chambered heart.

Renal portal system is lacking.

RBCs are circular, biconcave and enucleated in most species.

Cranial nerves

10 pairs of cranial nerves.

12 pairs of cranial nerves.

Brain is large with well-developed optic lobes, cerebellum and reduced olfactory lobes.

There are 12 pairs of cranial nerves.

Brain has large cerebrum and cerebellum.

Corpus callosum connects the two halves of the cerebrum.

There are 12 pairs of cranial nerves.

Sense organs

Olfactory sacs communicate with buccopharyngeal cavity by internal nares.

Eyes have movable and transparent lids (nictitating membrane).

No external ear.

Lateral line system in larvae and aquatic forms.

Olfactory sacs communicate with buccopharyngeal cavity by internal nares.

Eyes have movable and transparent lids (nictitating membrane).

Ears have single auditory ossicles. External ear may be present.

Lateral line sense organs are absent.

Olfactory sacs open by internal nares into buccal cavity.

Sense of smell is poor.

Eyes are usually large and have keen eyesight.

Ears have an external openings and large, curved cochlea with organ of Corti.

Olfactory sacs open by internal nares far back into pharynx.

Eyes have movable eye lids.

Internal ear has organ of Corti.

Middle ear has three bony ear ossicles.

Excretory
system

Kidneys are opisthonephric.

Waste material is removed as urea in tailless forms (ureotelism) and ammonia in larvae and tailed form (ammonotelism).

Kidneys are metanephric.

Uric acid in land forms (uricotelism) and as urea in aquatic forms.

Kidneys are metanephric.

Excretory matter is chiefly uric acid.

No urinary bladder.Rhea americana is the only bird to have a urinary bladder.

Kidneys are metanephric and bean shaped.

Excretes urea.

Reproductive system

Gonoducts lead into cloaca.

Males lack copulatory organ.

Fertilisation may be external or internal.

Most forms are oviparous.

Life history includes an aquatic larva which undergoes metamorphosis.

Gonoducts lead into cloaca. Fertilisation is external. Mostly oviparous but some are ovoviviparous. Eggs are amniotic with abundant yolk and leathery or shiny shell.

Exhibits sexual dimorphism.

Testes are paired.

Right ovary and oviduct are absent.

Gonoducts lead into cloaca.

Oviparous.

Amniotic egg with hard, calcareous shell.

Development is direct.

Sexual dimorphism observed. Gonoducts lead directly into the exterior.

Fertilisation is internal.

Mammals are viviparous.

Development takes place in uterus of female and is direct.

Temperature

Poikilothermy.

Most forms hibernate in winter and aestivate in summer.

Poikilothermy.

Homeothermy.

Homeothermy.

Examples

Ichthyopis (limbless amphibian), Rana tigerina (common Indian frog), Bufo (common Indian toad), salamander.

Chamaeleon, draco,Naja, python, chelone (turtle), testudo (tortoise), alligator.

Flying birds: Columba(pigeon), pavo (peacock).

flightless birds:Struthio (ostrich), Apteryx (kiwi).

Prototherians: duck billed platypus.

Metatherians (marsupials): kangaroo, opossum.

Eutherians (placentals): human, elephant.

Others

Age of amphibians is the carboniferous period.

Golden age of reptiles is the mesozoic era.

Archeopteryx is the connecting link between aves and reptiles.

Golden age of mammals is the Cenozoic era.

 





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