Definition: Chordates are animals possessing a notochord, a hollow dorsal nerve cord, pharyngeal slits, and a post-anal tail at some point in their life cycle.
Characteristics:
Notochord: A flexible, rod-shaped structure found in the embryonic stage of all chordates.
Dorsal Nerve Cord: Develops into the brain and spinal cord.
Pharyngeal Slits: Openings in the pharynx that develop into gill structures in aquatic chordates.
Post-Anal Tail: Extension of the body past the anal opening.
2. Classification of Chordates
Three Subphyla:
Urochordata (Tunicates):
Marine organisms.
Notochord present only in the larval stage.
Examples: Sea squirts.
Cephalochordata (Lancelets):
Marine organisms.
Notochord extends throughout life.
Examples: Amphioxus.
Vertebrata (Craniata):
Have a vertebral column.
Includes fishes, amphibians, reptiles, birds, and mammals.
3. Subphylum Vertebrata
Characteristics:
Endoskeleton: Made of cartilage or bone.
Complex Nervous System: Highly developed brain enclosed in a skull.
Closed Circulatory System: Heart with two, three, or four chambers.
Excretory System: Kidneys filter waste products from the blood.
4. Classes of Vertebrates
Agnatha (Jawless Fishes):
Lack jaws and paired fins.
Examples: Lampreys, hagfish.
Chondrichthyes (Cartilaginous Fishes):
Skeleton made of cartilage.
Examples: Sharks, rays.
Osteichthyes (Bony Fishes):
Skeleton made of bone.
Examples: Salmon, goldfish.
Amphibia (Amphibians):
Dual life: aquatic larval stage and terrestrial adult stage.
Examples: Frogs, salamanders.
Reptilia (Reptiles):
Scaly skin, lay shelled eggs.
Examples: Snakes, lizards, turtles.
Aves (Birds):
Feathers, beak, lay eggs, endothermic.
Examples: Eagles, sparrows.
Mammalia (Mammals):
Hair or fur, mammary glands, endothermic.
Examples: Humans, whales, elephants.
5. Adaptations in Chordates
Respiratory Adaptations:
Gills in fishes.
Lungs in amphibians, reptiles, birds, and mammals.
Reproductive Adaptations:
Oviparous (egg-laying) and viviparous (live-bearing) species.
Locomotory Adaptations:
Fins in fishes.
Limbs in amphibians, reptiles, birds, and mammals.
Sensory Adaptations:
Highly developed eyes, ears, and olfactory systems.
6. Examples and Economic Importance
Fishes: Important for food, sport, and aquarium trade.
Amphibians: Indicators of environmental health, pest control.
Reptiles: Control rodent populations, some are pets.
Birds: Pollination, seed dispersal, pest control, food.
Mammals: Domesticated animals for food, labor, and companionship.
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