Classification of the Animal Kingdom

Study Notes

Kingdom Animalia is one of the five kingdoms of living organisms: plants, fungi, protista, monera, and animalia.
Animals are multi-cellular and cannot produce their own food, distinguishing them from plants.
Animal cells lack cell walls, making them visually different from other life kingdoms.
The animal kingdom is the largest, with many diverse species present in various environments around the globe.

Animals are classified into two main groups: vertebrates (species with a backbone) and invertebrates (species without a backbone).
Invertebrates comprise approximately 97% of all animal species, with over a million identified and many millions more estimated to exist.
Vertebrates include around 60,000 known species and are categorized under the phylum Chordata.

Fish:
- Live in water, breathe through gills, covered in scales, and are ectothermic.
- Most reproduce externally by laying fertilized eggs outside their bodies.
Amphibians:
- Examples include frogs and toads.
- Begin life as larvae in water, breathing through gills; undergo metamorphosis to become adults.
- Adults have lungs and can absorb water through their skin, allowing them to hibernate underwater.
- Also ectothermic, with external reproduction.
Reptiles:
- Include snakes, turtles, lizards, crocodiles, and extinct dinosaurs.
- Ectothermic, scaly, and breathe air using lungs.
- Reproduce internally; eggs are fertilized within the female and typically laid outside.
Birds:
- Closely related to reptiles, characterized by feathers and endothermic nature.
- Maintain a constant warm body temperature regardless of the environment.
- Generally, birds can fly, but some, like penguins and ostriches, are flightless.
Mammals:
- Endothermic, breathe via lungs, and most reproduce internally, giving birth to live young instead of laying eggs.
- Unique for feeding young with milk from specialized glands.
- Varied environments: while many are hairy and terrestrial, others like whales are smooth-skinned and aquatic; some mammals like bats can fly.
- Humans are classified as mammals in the order of primates and family of great apes.

Body	Breathing	Skin	Reproduction	Other Features
Fish	Gills	Scales	External, lay eggs	Ectothermic
Amphibians	Gills (larvae), lungs	Moist skin	External, undergo metamorphosis	Ectothermic
Reptiles	Lungs	Scales	Internal fertilization, lay eggs	Ectothermic
Birds	Lungs	Feathers	Lay eggs	Endothermic
Mammals	Lungs	Hair	Internal, live birth	Milk feeding to young