Introduction

Phylum Chordata includes animals that possess a notochord at some stage of their life cycle. It is the phylum that contains vertebrates, including fish, amphibians, reptiles, birds, and mammals.

Distinguishing Features of Phylum Chordata

  1. Chordates exhibit bilateral symmetry.
  2. They are triploblastic and have a well-developed coelom (coelomates).
  3. Possess a notochord, at least in the embryonic stage.
  4. Have a dorsal hollow nerve cord running along the body.
  5. Presence of pharyngeal gill slits in some stage of life.
  6. Exhibit a post-anal tail for movement and balance.
  7. Well-developed closed circulatory system.
  8. Have a ventral heart (positioned towards the front).
  9. Respiration occurs through gills, lungs, or skin, depending on the class.
  10. Most have a well-developed brain enclosed in a skull.

Subphyla of Chordata

1. Subphylum Urochordata (Tunicates)

  1. Also called Tunicata.
  2. Notochord is present only in the larval stage.
  3. Adult body is covered by a protective tunic.
  4. Marine filter feeders.
  5. Examples: Ascidia, Salpa, Doliolum.

2. Subphylum Cephalochordata (Lancelets)

  1. Also called Amphioxus.
  2. Notochord persists throughout life.
  3. Small, fish-like marine animals.
  4. Respiration occurs through the body surface.
  5. Example: Branchiostoma (Lancelet).

3. Subphylum Vertebrata

  1. Possess a vertebral column replacing the notochord.
  2. Distinct head and well-developed brain.
  3. Complex internal organ systems.
  4. Divided into five classes: Pisces, Amphibia, Reptilia, Aves, Mammalia.

Key Features of Vertebrates

  1. Have a cartilaginous or bony endoskeleton.
  2. Respiration occurs through gills, lungs, or skin.
  3. Highly advanced nervous system.
  4. Presence of a closed circulatory system with hemoglobin.
  5. Excretion through kidneys.
  6. Sexes are separate (dioecious) in most vertebrates.
  7. Internal or external fertilization.
  8. Development can be oviparous (egg-laying) or viviparous (live birth).

Classification of Vertebrates

1. Class Pisces (Fishes)

  1. Aquatic animals with gills for respiration.
  2. Body covered with scales.
  3. Exothermic (cold-blooded).
  4. Two-chambered heart.
  5. Examples: Shark, Rohu, Sea horse.

2. Class Amphibia

  1. Live both in water and land.
  2. Respiration through lungs, gills, and skin.
  3. Cold-blooded, three-chambered heart.
  4. Undergo metamorphosis.
  5. Examples: Frog, Toad, Salamander.

3. Class Reptilia

  1. Terrestrial animals with scaly skin.
  2. Cold-blooded, three-chambered heart (except crocodiles with four chambers).
  3. Internal fertilization, mostly oviparous.
  4. Examples: Snake, Lizard, Crocodile, Turtle.

4. Class Aves (Birds)

  1. Body covered with feathers.
  2. Forelimbs modified into wings.
  3. Warm-blooded, four-chambered heart.
  4. Respiration through lungs with air sacs.
  5. Examples: Parrot, Eagle, Pigeon.

5. Class Mammalia

  1. Body covered with hair or fur.
  2. Possess mammary glands for milk production.
  3. Warm-blooded, four-chambered heart.
  4. Respiration through lungs.
  5. Mostly viviparous (except monotremes like Platypus).
  6. Examples: Humans, Elephants, Whales, Dogs.

Additional Key Points

  1. All chordates have a notochord at some stage of life.
  2. Vertebrates are the most evolved organisms in the animal kingdom.
  3. Cephalochordates are simple marine organisms retaining chordate features throughout life.
  4. Urochordates lose their notochord in adulthood.
  5. Chordates are the only animals with a dorsal hollow nerve cord.
  6. Vertebrates have complex organ systems for higher survival adaptability.

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