Animal Kingdom: Vertebrates

Animal Kingdom: Vertebrates

Table of Content

Definition of Vertebrates

Vertebrates represents the phylum Chordata. There are about 64,000 species known in this group. It includes jawless fishes and jawed vertebrates.

Anatomy and Morphology of Vertebrates/Vertebrates Characteristics

  • Notochord found in chordates are replaced by segmented series of elements known as vertebrae.
  • All basal vertebrates used gills for respiration, such as fishes. But higher vertebrates lack gills. They have lungs for respiration.
  • Central nervous system is hollow with dorsal nerve cord. Vertebrates are only chordates with cephalization (brain is concentrated in head region).
  • All vertebrates have ventral, muscular heart with a closed circulatory system.
  • Reproduction is usually sexual.
  • They are unisexual animals with a pair of gonads.
  • They possess two pairs of appendages.
  • Presence of paired pharyngeal gill slits.
  • They are bilaterally symmetrical.
  • Triploblastic in nature.
  • They are coelomate with well- developed organ system and organization.
  • They possess post anal tail at some or the other stages of life.
  • Kidneys are excretory organs which maintains the osmoregulation of the body.

Classification of Vertebrates

Phylum Chordata is divided into- Urochordata or Tunicata, Cephalochordata and Vertebrata.

Classification of vertebrates

Fig.1. Classification of vertebrates

Agnatha/Vertebrates lower Classification

  • Is a superclass of jawless fish.
  • It comprises of both cyclostomes and extinct conodonts and ostracoderms.
  • They have notochord in larval and adult stages.
  • They are characterized by absence of paired fins.
  • They are cold-blooded with cartilaginous skeleton.
  • The heart is two chambered.

For example, Myxine (Hagfish) and Petromyzon (Lamprey).

Cyclostomes- Hagfish and Lamprey

Fig.2. Cyclostomes- Hagfish and Lamprey


It includes subclass- Chondrichthyes and Osteichthyes


  • Cartilaginous fishes are included in this subclass.
  • Notochord persist throughout the life.
  • Gill slits are present but without gill cover (operculum).
  • Presence of Placoid scales.
  • They are predatory animals.
  • Absence of air bladder due to which they swim continuously.
  • They possess two chambered heart with one auricle and one ventricle.
  • Electric organs are present in Torpedo.
  • Some have poison sting such as Trygon.
  • They have separate sexes.
  • Internal fertilization and generally viviparous.

(a) Scolidon (b)-Pristis

Fig.3. (a)-Scolidon (b)-Pristis

For example, Carcharodon (Great white shark), Trygon (Sting ray), Scoliodon (Dog fish) etc.


  • Marine as well as freshwater fishes are included in this subclass.
  • They have bony endoskeleton.
  • They have gill with operculum.
  • Skin is with Ctenoid scales.
  • They are cold-blooded animals.
  • Presence of air bladder.
  • Heart is two chambered with one auricle and one ventricle.
  • External fertilization and organisms are oviparous in nature.

(a) Hippocampus (b) Catla

Fig.4. (a) Hippocampus (b) Catla

For example, Pterophyllum (Angel fish), Hippocampus (Sea horse), Freshwater – Labeo (Rohu)

Class – Amphibia

  • They live in aquatic as well as in terrestrial environment.
  • Possess two pairs of limbs.
  • Body is divided into head and trunk.
  • Skin is without scales.
  • Eyes possess eyelids.
  • Cloaca is the common opening of alimentary canal, urinary and reproductive tract.
  • Gills, lungs, and skin acts as respiratory organs.
  • Heart is three chambered with two auricles and one ventricle.
  • Fertilization occurs in water, that is, external.
  • Sexes are separate with indirect development.
  • They are oviparous in nature.


Fig.5. Amphibians

For example, Salamandra (Salamander), Bufo (Toad), Rana (Frog) etc.

There are three subclasses of Amphibia are- Labyrinthodontia, Lepospondyli and Lissamphibia.

Subclass Lissamphibia consists of three orders-

  • Caudata- For example, Salamander.
  • Anura- For example, Frogs and toads.
  • Apoda- For example, Caecilians.

Class- Reptilia

  • They have crawling mode of locomotion.
  • Mostly they are terrestrial in nature.
  • They have dry cornified skin with epidermal scales or Scutes.
  • They are without external ear openings.
  • Heart is three chambered but some have four chambered heart such as Crocodiles.
  • They have the ability to regulate their body temperature, that is, Poikilotherms.
  • Sexes are separate with internal fertilization.
  • Development is direct and oviparous in nature.


Fig.6. Reptilia

For example, Crocodilus (Crocodile), Testudo (Tortoise), Alligator (Alligator), Hemidactylus (Wall lizard), Poisonous snakes – Naja (Cobra)

Subclasses of Reptilia are as follows- Anapsida, Parapsida, Diapsida and Synapsida.

  • Subclass Anapsida includes order Chelonia. For example, Tortoise and Turtles.
  • Subclass Parapsida, for example, Protosaurs.
  • Subclass Diapsida includes orders such as Rhyncocephalia (tuatara), Squamata (Lizards and snakes) and Crocodilia (Crocodiles).
  • Synapsida, for example, ss.

Class – Aves

  • Characteristic feature is the presence of feathers in all birds except flightless birds.
  • They have beak.
  • They have forelimbs which are modified into wings.
  • Hind limbs serve for walking, clasping and swimming.
  • Presence of oil glands at the base of the tail.
  • Endoskeleton is bony with hollow long bones. Hollow bones helps during flight.
  • Birds have additional chambers in digestive system known as crop and gizzard.
  • Heart is four chambered with two auricles and two ventricles.
  • They are warm-blooded animals.
  • Lungs are respiratory organs.
  • Fertilization is internal with separate sexes.
  • Development is direct and oviparous in nature.


Fig.7. Aves

For example, Aptenodytes (Penguin), Neophron (Vulture), Corvus (Crow), Columba (Pigeon)

There are basically two subclasses- Archeornithes and Neornithes.

The subclass Archeornithes includes single genus fossil bird having a single species, Archaeopteryx lithograpthica.

Neornithes includes Odontognathae and Neognathae.

Class – Mammalia

  • They are adapted for polar environment, deserts, forests, mountains, grasslands, and dark caves.
  • The most important feature is presence of milk producing glands known as mammary glands.
  • They possess two pairs of limbs which are adapted for walking, jumping, climbing, burrowing, swimming, flying, and running.
  • Presence of characteristics hairs on the skin.
  • Presence of external ear known as Pinnae.
  • Heart is four chambered with two auricles and two ventricles.
  • They maintain their constant body temperature, so considered as homoiothermous.
  • Lungs are the respiratory organs.
  • Development is direct with viviparous nature.
  • Fertilization is internal.

(a) Ornithorhynchus (b) Macropus (c) Pteropus (d) Balaenoptera

Fig.8. (a) Ornithorhynchus (b) Macropus (c) Pteropus (d) Balaenoptera

For example, Rattus (Rat), Canis (Dog), Felis (Cat), Macropus (Kangaroo), Pteropus (Flying fox), Camelus (Camel), Oviparous-Ornithorhynchus (Platypus)

Subclasses of Mammalia

Watch this Video for more reference

More Readings

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