Quick Summary
Kingdom Animalia contains multicellular, eukaryotic, heterotrophic organisms. Animals are classified by increasingly complex body plans — from sponges (cellular level) to chordates (organ system level). Nine major non-chordate phyla and the Chordata phylum with its five vertebrate classes must be known for NEET.
Basis of Classification
| Character | Types |
|---|---|
| Level of organisation | Cellular → Tissue → Organ → Organ system |
| Symmetry | Asymmetry (sponges), Radial (Coelenterata), Bilateral (most) |
| Coelom | Acoelomate, Pseudocoelomate, Coelomate (true) |
| Segmentation | Metamerism (Annelida, Arthropoda) |
| Notochord | Absent (non-chordates), Present (Chordata) |
Non-Chordate Phyla
Phylum Porifera (Sponges)
- Level: Cellular
- Symmetry: Asymmetrical
- Coelom: Absent
- Features: Pores (ostia), osculum, canal system, choanocytes (collar cells), spicules or spongin fibres
- Examples: Sycon, Spongilla (freshwater), Euspongia
Phylum Coelenterata (Cnidaria)
- Level: Tissue
- Symmetry: Radial
- Features: Cnidoblasts (nematocysts — stinging), diploblastic, gastrovascular cavity, polymorphism (polyp + medusa forms)
- Examples: Hydra, Aurelia (jellyfish), Adamsia (sea anemone), corals
Phylum Platyhelminthes (Flatworms)
- Level: Organ
- Symmetry: Bilateral
- Coelom: Acoelomate
- Features: Triploblastic, flat body, flame cells for excretion, hermaphrodite, mostly parasitic
- Examples: Planaria (free-living), Fasciola (liver fluke), Taenia (tapeworm)
Phylum Aschelminthes / Nematoda (Roundworms)
- Coelom: Pseudocoelomate
- Features: Cylindrical body, cuticle, complete digestive tract, separate sexes
- Examples: Ascaris (roundworm), Wuchereria (filarial worm — elephantiasis), Ancylostoma (hookworm)
Phylum Annelida (Segmented Worms)
- Coelom: True coelomate
- Features: Metamerism (true segmentation), nephridia (excretion), setae, closed circulatory system
- Examples: Pheretima (earthworm), Nereis, Hirudinaria (leech)
Phylum Arthropoda (Largest phylum)
- Features: Jointed appendages, exoskeleton (chitin), open circulatory system, compound eyes, Malpighian tubules (excretion)
- Examples: Apis (bee), Bombyx (silkworm), Cancer (crab), Scolopendra (centipede), Periplaneta (cockroach), Limulus (king crab — living fossil)
Phylum Mollusca (Second largest)
- Features: Soft body, mantle, radula (rasping organ), mostly with shell
- Examples: Pila (apple snail), Pinctada (pearl oyster), Sepia (cuttlefish), Loligo (squid), Octopus
Phylum Echinodermata
- Features: Water vascular system, tube feet, endoskeleton of calcareous ossicles, radial symmetry (adults), bilateral (larvae), triploblastic coelomate, regeneration
- Examples: Asterias (starfish), Echinus (sea urchin), Holothuria (sea cucumber), Feather star
Phylum Chordata
Three defining characters (all present at some stage): 1. Notochord — flexible rod 2. Dorsal hollow nerve cord 3. Paired pharyngeal gill slits Also: ventral heart, post-anal tail
Vertebrate Classes
| Class | Features | Examples |
|---|---|---|
| Pisces (Fish) | Aquatic, gills, scales, cold-blooded, 2-chambered heart | Rohu, shark, flying fish |
| Amphibia | Dual life (water + land), moist skin, cold-blooded, 3-chambered heart | Frog, toad, salamander |
| Reptilia | Scales, lungs, cold-blooded, 3-chambered heart (crocodile: 4) | Snake, lizard, crocodile, tortoise |
| Aves (Birds) | Feathers, hollow bones, warm-blooded, 4-chambered heart, flight (mostly) | Pigeon, ostrich, penguin |
| Mammalia | Hair/fur, mammary glands, warm-blooded, 4-chambered heart, live birth (mostly) | Human, whale, bat, platypus |
Important Questions
One Mark
- Which is the largest phylum in the animal kingdom?
- Name the excretory organ in Annelida.
- What are cnidoblasts?
- Name an acoelomate animal.
Short Answer (3 marks)
- Compare Porifera and Coelenterata on the basis of level of organisation, symmetry, and feeding.
- Distinguish between pseudocoelom and true coelom with examples.
- Write the salient features of Phylum Echinodermata with two examples.
Long Answer (5 marks)
- Write the three defining characters of Phylum Chordata. Describe the five vertebrate classes with one example each.
- Compare non-chordates and chordates on the basis of five characters.
Common Mistakes
- Arthropoda is the largest phylum (not Chordata or Annelida).
- Coelenterata = Cnidaria — both names are used; know either.
- Platyhelminthes are acoelomate (no coelom), Aschelminthes are pseudocoelomate (false coelom), Annelida onwards are true coelomates.
- Aves: 4-chambered heart, warm-blooded (endothermic) — not cold-blooded.
Board Exam Tips
- Vertebrate class comparison table (5 classes, 4–5 characters) is a standard 5-mark question.
- Phylum features + 2 examples for 3–4 phyla is a common 5-mark question.
- Chordata's three defining features must be memorised — they appear as a 1-mark or 2-mark question.
- NEET: Animal kingdom classification contributes 3–5 questions per paper — highest yield zoology topic.
Frequently Asked Questions
Level of organisation, symmetry (radial/bilateral), coelom (acoelomate/pseudocoelomate/coelomate), segmentation, notochord. These characters are used to classify animals into phyla.