⚡ Quick Revision: Basis of Animal Classification
Kingdom Animalia includes multicellular, heterotrophic organisms. They are primarily classified based on the presence or absence of a backbone (vertebral column).
Invertebrates: Animals without a backbone (make up 95% of the animal kingdom).
Vertebrates: Animals with a backbone.
Key Characteristics used for Classification
- ✔ Body Symmetry: Asymmetrical (sponges), Radial (starfish), or Bilateral (humans).
- ✔ Body Cavity (Coelom): Presence or absence of a fluid-filled cavity between the body wall and digestive tract.
- ✔ Level of Organization: Cellular, Tissue, or Organ-system level.
⚡ Quick Revision: Lower Invertebrates
These groups represent animals with simpler body designs, ranging from cellular colonies to primitive organ systems.
Phylum Comparison (Part 1)
| Phylum | Key Characteristics | Examples |
|---|---|---|
| Porifera | Pore-bearing bodies; sedentary (don't move); cellular level of organization. | Sycon, Spongilla (Sponges). |
| Cnidaria (Coelenterata) | Hollow body cavity; possess stinging cells (cnidoblasts) for defense. | Hydra, Jellyfish, Sea Anemone. |
| Platyhelminthes | Dorso-ventrally flat bodies; mostly parasites; bilateral symmetry. | Tapeworm, Liver fluke, Planaria. |
| Nematoda (Aschelminthes) | Cylindrical, unsegmented round bodies; complete digestive tract. | Ascaris (Roundworm), Wuchereria. |
While Sponges are mostly Asymmetrical, Cnidarians show Radial Symmetry (can be cut into equal halves along any plane through the center).
⚡ Quick Revision: Higher Invertebrates
These groups show complex organ systems, specialized movement, and in some cases, hard protective coverings.
Phylum Comparison (Part 2)
| Phylum | Key Characteristics | Examples |
|---|---|---|
| Annelida | Segmented ring-like bodies; have a true coelom (body cavity). | Earthworm, Leech. |
| Arthropoda | Jointed legs; Exoskeleton made of chitin; Largest phylum. | Cockroach, Butterfly, Crab, Scorpion. |
| Mollusca | Soft-bodied; often have a calcareous shell; Muscular foot for movement. | Snail, Octopus, Pila. |
| Echinodermata | Spiny-skinned; Radial symmetry (adults); Marine only. | Starfish, Sea Urchin. |
Arthropoda is further divided into classes like Insecta (6 legs), Arachnida (8 legs), and Crustacea. They are highly successful due to their protective exoskeleton.
⚡ Quick Revision: Vertebrates (Part 1)
Vertebrates are characterized by an internal skeleton and a backbone. Most show highly developed nervous systems and sense organs.
Cold-Blooded Classes
Poikilotherms: Animals whose body temperature changes with the environment.
| Class | Skin / Respiration | Heart Chambers | Examples |
|---|---|---|---|
| Pisces (Fish) | Scaly skin; Breathe through Gills. | 2 Chambers. | Shark, Rohu, Catla. |
| Amphibia | Moist, slimy skin; Gills (larva) & Lungs (adult). | 3 Chambers. | Frog, Toad, Salamander. |
| Reptilia | Dry, scaly skin; Breathe through Lungs. | 3 Chambers (4 in Crocodiles). | Snake, Lizard, Turtle. |
Most members of these three classes are Oviparous (lay eggs). Amphibians must return to water to lay their eggs, while reptiles lay leathery eggs on land.
⚡ Quick Revision: Vertebrates (Part 2)
Homeotherms: Animals that maintain a constant body temperature regardless of the external environment. This allows them to live in diverse climates.
Aves vs. Mammalia
| Feature | Class Aves (Birds) | Class Mammalia (Mammals) |
|---|---|---|
| Body Covering | Covered with Feathers. | Covered with Hair/Fur. |
| Heart | 4 Chambers. | 4 Chambers. |
| Reproduction | Oviparous (Lay hard-shelled eggs). | Viviparous (Give birth to young ones). |
| Unique Feature | Hollow bones; Wings for flight. | Presence of Mammary glands to feed young. |
| Examples | Pigeon, Sparrow, Ostrich. | Human, Tiger, Whale, Bat. |
The Duck-billed Platypus and Echidna are mammals that lay eggs. Bats are mammals that can fly, and Whales/Dolphins are mammals that live in water.