Introduction to Chordates and Non-Chordates

Non-Chordates

• Nerve cord, if present, is located on the ventral side and is solid and paired.
• Heart, if present, is located on the dorsal side.
• Non-chordates classified into ten phyla:
  • Protozoa
  • Porifera
  • Cnidaria
  • Platyhelminthes
  • Aschelminthes
  • Annelida
  • Arthropoda
  • Mollusca
  • Echinodermata
  • Hemichordata

Chordates

• Characterized by a notochord that supports the body.
• Presence of pharyngeal gill-slits or lungs for respiration.
• Dorsal nerve cord is hollow.
• Heart situated on the ventral side.

Phylum Chordata

• All chordates are grouped under Phylum-Chordata.
• Divided into three subphyla:
  • Urochordata
  • Cephalochordata
  • Vertebrata
• Vertebrata further divided into six classes:
  • Cyclostomata
  • Pisces
  • Amphibia
  • Reptilia
  • Aves
  • Mammalia

Body Symmetry

• Animals can be classified based on body symmetry:
  • Asymmetrical: No imaginary axis; e.g., sponges.
  • Radial Symmetry: Any plane through the central axis yields equal halves; e.g., starfish.
  • Bilateral Symmetry: One imaginary axis results in two equal halves; e.g., humans, frogs, fish.

Germ Layers

• Multicellular animals develop germ layers during embryonic development:
  • Diploblastic: Two germ layers (ectoderm and endoderm); e.g., Cnidarians.
  • Triploblastic: Three germ layers (ectoderm, mesoderm, endoderm); present in most other animals.

Body Cavity (Coelom)

• Coelom is the body cavity between the body wall and internal organs.
• True body cavity (eucoelom) is found in phyla like Annelida and those after it.

Class Characteristics

• Class Amphibia:

  • First group of true terrestrial animals.
  • Cold-blooded (poikilotherms).
  • Skin is moist and lacks external ears but has a tympanum.
  • Examples: Frog, Toad, Salamander.

• Class Reptilia:

  • First true terrestrial animals with scaly, dry skin.
  • Cold-blooded and cannot lift their body off the ground.
  • Neck is present between head and trunk.
  • Examples: Tortoise, Lizard, Snake.

• Class Aves:

  • Fully adapted for aerial life; warm-blooded (homeotherms).
  • Body shape minimizes air resistance.
  • Forelimbs modified into wings with feathers for exoskeleton.
  • Examples: Peacock, Parrot, Pigeon.

• Class Mammalia:

  • Presence of mammary glands.
  • Warm-blooded with a body divided into head, neck, trunk, and tail.
  • Digits may have nails, claws, or hooves, exoskeleton in the form of hair or fur.
  • Examples: Elephant, Human, Dolphin, Bat.

Additional Notes

• Animals like gharial and crocodile are reptiles, despite their semi-aquatic lifestyle.
• Whales and walruses, living in the ocean, belong to the class Mammalia.
• Importance of responsible animal study highlighted, warning against harm during observations.