Animal Kingdom: Vertebrates

Table of Content

• Definition of Vertebrates
• Anatomy and Morphology of Vertebrates
• Classification of Vertebrates
• Agnatha/ Vertebrates lower Classification
• Class-Pisces
• Class – Amphibia
• Class- Reptilia
• Class – Aves
• Class – Mammalia

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.

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).

Fig.2. Cyclostomes- Hagfish and Lamprey

Class-Pisces

It includes subclass- Chondrichthyes and Osteichthyes

Chondrichthyes

• 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.

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

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

Osteichthyes

• 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.

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.

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

• Subclass Eutheria (Placental mammals).
• Subclass Metatheria (marsupials).
• Subclass Prototheria.

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