Classification of Animals
1. The Animal Kingdom
The Animal Kingdom (Animalia) includes ALL multicellular organisms that are HETEROTROPHIC (cannot make their own food).
Basis of Classification
Animals are classified based on:
- Presence or absence of BACKBONE (vertebrate vs invertebrate).
- Body organisation (cellular, tissue, organ).
- Body symmetry (radial, bilateral, asymmetrical).
- Number of body layers (diploblastic, triploblastic).
- Presence of body cavity (coelom).
2. Phylum Porifera (Sponges)
Meaning: 'Pore-bearers' (Latin: porus = pore, ferre = to bear).
| Feature | Description |
|---|---|
| Habitat | Aquatic (mostly MARINE) |
| Body | Porous body with OSTIA (small pores) and OSCULUM (large opening) |
| Symmetry | ASYMMETRICAL |
| Organisation | Cellular level (no true tissues) |
| Support | SPICULES (needle-like structures) |
| Examples | Sponge, Sycon, Euspongia (bath sponge) |
3. Phylum Cnidaria (Coelenterata)
Features: Stinging cells (CNIDOBLASTS or NEMATOCYSTS) for defence and capturing prey.
| Feature | Description |
|---|---|
| Habitat | Aquatic (mostly marine) |
| Body | Two body forms: POLYP (sessile) and MEDUSA (free-swimming) |
| Symmetry | RADIAL |
| Organisation | Tissue level |
| Body cavity | Single opening (mouth) — gastrovascular cavity |
| Examples | Hydra, Jellyfish, Coral, Sea anemone |
4. Phylum Platyhelminthes (Flatworms)
Meaning: 'Flat worms' (platy = flat, helminth = worm).
| Feature | Description |
|---|---|
| Body | FLATTENED dorsoventrally (ribbon-like) |
| Symmetry | BILATERAL |
| Organisation | Organ level |
| Body cavity | NO body cavity (acoelomate) |
| Examples | Planaria (free-living), Tapeworm (Taenia — parasitic), Liver fluke (Fasciola) |
5. Phylum Nematoda (Roundworms)
Meaning: 'Thread-like worms' (nema = thread).
| Feature | Description |
|---|---|
| Body | CYLINDRICAL, tapered at both ends |
| Symmetry | BILATERAL |
| Body cavity | PSEUDOCOELOM (false body cavity) |
| Examples | Ascaris (roundworm in intestines), Wuchereria (filarial worm — elephantiasis), Hookworm |
6. Phylum Annelida (Segmented Worms)
Meaning: 'Ringed worms' (annulus = little ring).
| Feature | Description |
|---|---|
| Body | SEGMENTED (divided into rings) |
| Symmetry | BILATERAL |
| Body cavity | TRUE coelom |
| Examples | Earthworm, Leech, Nereis (ragworm) |
7. Phylum Arthropoda (Jointed Legs)
Meaning: 'Jointed feet' (arthros = joint, podos = foot). LARGEST phylum in the animal kingdom.
| Feature | Description |
|---|---|
| Body | Segmented into HEAD, THORAX, ABDOMEN |
| Appendages | JOINTED legs and appendages |
| Exoskeleton | Made of CHITIN |
| Symmetry | BILATERAL |
| Examples | Insects (butterfly, ant, bee), Crustaceans (crab, prawn), Arachnids (spider, scorpion), Myriapods (centipede, millipede) |
8. Phylum Mollusca (Soft-Bodied Animals)
Meaning: 'Soft body' (mollis = soft).
| Feature | Description |
|---|---|
| Body | SOFT, unsegmented. Often with a HARD SHELL |
| Body parts | Head, foot, visceral mass, mantle |
| Examples | Snail, Octopus, Squid, Mussel, Oyster |
9. Phylum Echinodermata (Spiny-Skinned)
Meaning: 'Spiny skin' (echinos = spiny, derma = skin).
| Feature | Description |
|---|---|
| Habitat | Strictly MARINE |
| Body | RADIAL symmetry (usually 5-fold) |
| Locomotion | WATER VASCULAR SYSTEM with tube feet |
| Examples | Starfish, Sea urchin, Sea cucumber, Brittle star |
10. Phylum Chordata (Animals with Backbone)
Animals with a NOTOCHORD (flexible rod) at some stage.
Subphylum: Vertebrata (Backbone present)
| Class | Features | Examples |
|---|---|---|
| Pisces (Fish) | Aquatic, scales, gills, 2-chambered heart | Rohu, Shark, Goldfish |
| Amphibia | Live on land AND water, moist skin, 3-chambered heart | Frog, Toad, Salamander |
| Reptilia | Dry scaly skin, lay eggs on land, 3-chambered heart | Lizard, Snake, Crocodile, Turtle |
| Aves (Birds) | Feathers, wings, beak, lay eggs, 4-chambered heart, WARM-BLOODED | Crow, Eagle, Parrot, Hen |
| Mammalia | Hair/fur, give birth (mostly), feed milk, 4-chambered heart, WARM-BLOODED | Human, Dog, Whale, Bat |
11. ICSE Exam Focus
| Topic | Marks | Frequency |
|---|---|---|
| Characteristics of each phylum | 3 marks | Very High |
| Vertebrate classes (compare) | 3 marks | Very High |
| Examples of each phylum | 2 marks | High |
| Invertebrate vs Vertebrate | 2 marks | Medium |
| Identifying phylum from features | 2 marks | Medium |
Common Mistakes
- Calling sponges 'plants' — they are ANIMALS (phylum Porifera).
- Confusing arthropod classes (insects have 3 body parts, 6 legs; arachnids have 2 body parts, 8 legs).
- Amphibia need water for reproduction (not just for living).
- Whales and dolphins are MAMMALS, not fish.
Self-Test (5 Questions)
Q1. Which is the LARGEST phylum of animals? (1 mark)
- A) Mollusca
- B) Arthropoda
- C) Chordata
- D) Annelida
Q2. 'Name the phylum to which an earthworm belongs.' (1 mark)
Q3. 'List three characteristics of mammals.' (2 marks)
Q4. 'Give one example of: Cnidaria, Echinodermata, Mollusca.' (3 marks)
Q5. 'Differentiate between amphibians and reptiles.' (2 points) (2 marks)
Answers
A1. B) Arthropoda (over 1 million species). A2. Annelida. A3. Have hair/fur, feed milk to young (mammary glands), warm-blooded, give birth to live young (most have). (Any three.) A4. Cnidaria: Hydra / Jellyfish. Echinodermata: Starfish / Sea urchin. Mollusca: Snail / Octopus. A5. Amphibia: Moist skin, lay eggs in water, need water for reproduction. Reptiles: Dry scaly skin, lay eggs on land, do NOT need water for reproduction.
