Introduction

The subphylum Vertebrata is classified into five major classes: Pisces, Amphibia, Reptilia, Aves, and Mammalia. These classes differ based on their structural and physiological characteristics.

1. Class Pisces (Fishes)

  1. Aquatic vertebrates with gills for respiration.
  2. Body covered with scales (except in some species).
  3. Possess fins for locomotion.
  4. Cold-blooded (ectothermic) animals.
  5. Two-chambered heart.
  6. Exoskeleton made of scales and endoskeleton made of cartilage or bones.
  7. Fertilization can be external or internal.
  8. Divided into two main groups:
    • Cartilaginous fishes (Chondrichthyes): Skeleton made of cartilage (e.g., Shark, Rays).
    • Bony fishes (Osteichthyes): Skeleton made of bones (e.g., Rohu, Salmon, Tuna).

2. Class Amphibia

  1. First vertebrates to adapt to both aquatic and terrestrial life.
  2. Respiration occurs through gills, lungs, and skin depending on the life stage.
  3. Cold-blooded animals with a three-chambered heart.
  4. Undergo metamorphosis (e.g., tadpole to frog).
  5. Moist and smooth skin, lacking scales.
  6. Fertilization is mostly external.
  7. Examples: Frog, Toad, Salamander, Newt.

3. Class Reptilia

  1. First fully terrestrial vertebrates.
  2. Body covered with dry, scaly skin to prevent water loss.
  3. Respiration occurs through lungs.
  4. Possess a three-chambered heart (except crocodiles, which have a four-chambered heart).
  5. Cold-blooded animals.
  6. Most reptiles lay amniotic eggs on land (oviparous), while some are viviparous.
  7. Internal fertilization.
  8. Examples: Snake, Lizard, Crocodile, Turtle.

4. Class Aves (Birds)

  1. Body covered with feathers (unique feature).
  2. Forelimbs modified into wings for flight.
  3. Warm-blooded (endothermic) animals.
  4. Possess a four-chambered heart.
  5. Respiration through lungs with air sacs for efficient oxygen supply.
  6. Lightweight hollow bones (pneumatic bones) for flight adaptation.
  7. Oviparous (lay eggs with hard shells).
  8. Beak adapted to feeding habits (no teeth).
  9. Examples: Parrot, Eagle, Pigeon, Peacock, Ostrich.

5. Class Mammalia

  1. Most advanced vertebrates.
  2. Body covered with hair or fur.
  3. Possess mammary glands for milk production.
  4. Warm-blooded animals with a four-chambered heart.
  5. Respiration occurs through lungs.
  6. Most mammals are viviparous (give birth to live young), except monotremes.
  7. Well-developed nervous system and large brain.
  8. Divided into three subclasses:
    • Monotremes: Egg-laying mammals (e.g., Platypus, Echidna).
    • Marsupials: Pouched mammals (e.g., Kangaroo, Koala).
    • Placentals: Fully developed young at birth (e.g., Humans, Elephants, Dogs).

Additional Key Points

  1. Pisces are the only vertebrates with gills throughout life.
  2. Amphibians are the only vertebrates that undergo metamorphosis.
  3. Reptiles were the first to develop an amniotic egg for terrestrial life.
  4. Aves have highly efficient respiratory and circulatory systems for flight.
  5. Mammals are the only vertebrates with mammary glands for nurturing young.

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