Animal Kingdom
NCERT Line-by-Line Breakdown for NEET 2026
Unit 1: Diversity in Living WorldFrom the microscopic sponges to the gigantic blue whale, the Animal Kingdom (Metazoa) is incredibly diverse. To study them effectively, we classify them based on fundamental features like Symmetry, Coelom, and Body Organization.
1. Basis of Classification
🧬 Symmetry
- Asymmetrical: No plane divides it into equal halves (e.g., Sponges).
- Radial: Any plane passing through center divides it (e.g., Coelenterates, Ctenophores, Echinoderms).
- Bilateral: Only one plane divides it (e.g., Annelids, Arthropods).
🥥 Coelom (Body Cavity)
- Acoelomates: Absent (Platyhelminthes).
- Pseudocoelomates: Scattered pouches (Aschelminthes).
- Coelomates: True cavity lined by mesoderm (Annelida onwards).
2. Non-Chordates (Porifera to Hemichordata)
This group includes animals without a notochord. Let’s break them down by Phylum.
| Phylum | Key Feature (NEET Gem) | Examples |
|---|---|---|
| Porifera | Water canal system, Choanocytes (Collar cells). | Sycon, Spongilla, Euspongia |
| Coelenterata | Cnidoblasts (stinging cells). Polyp & Medusa forms (Metagenesis in Obelia). | Physalia, Adamsia, Aurelia |
| Ctenophora | Bioluminescence, 8 Comb plates. | Pleurobrachia, Ctenoplana |
| Platyhelminthes | Flattened body, Flame cells (Excretion). | Taenia (Tapeworm), Fasciola |
| Aschelminthes | Pseudocoelomate, Muscular pharynx. | Ascaris, Wuchereria |
| Annelida | Metameric segmentation, Parapodia (Nereis). | Pheretima (Earthworm), Hirudinaria |
| Arthropoda | Largest Phylum. Jointed appendages, Chitinous exoskeleton. | Apis, Bombyx, Laccifer, Limulus |
| Mollusca | 2nd Largest. Radula (rasping organ), Mantle cavity. | Pila, Octopus, Pinctada (Pearl oyster) |
| Echinodermata | Water vascular system. Larva is bilateral, Adult is radial. | Asterias (Starfish), Cucumaria |
| Hemichordata | Worm-like marine animals. Stomochord (rudimentary structure). | Balanoglossus, Saccoglossus |
3. Phylum Chordata
Characterized by the presence of a Notochord, dorsal hollow nerve cord, and paired pharyngeal gill slits.
⚠️ Vertebrata Division
Vertebrates are divided into Agnatha (Jawless) and Gnathostomata (Bear Jaws).
- Class Cyclostomata: Jawless, sucking mouth, 6-15 pairs of gill slits. (e.g., Petromyzon, Myxine).
Superclass: Pisces (Fish)
• Notochord persistent.
• Skin: Placoid scales.
• Air bladder absent (swim constantly).
• Ex: Scoliodon, Pristis, Torpedo.
• Terminal mouth.
• Skin: Cycloid/Ctenoid scales.
• Air bladder present (buoyancy).
• Ex: Labeo (Rohu), Hippocampus.
Superclass: Tetrapoda
| Class | Heart | Respiration | Unique Feature |
|---|---|---|---|
| Amphibia | 3-Chambered | Gills, Lungs, Skin | Dual life (Land+Water). Tympanum represents ear. |
| Reptilia | 3-Chambered (4 in Crocs) | Lungs | Dry, cornified skin with scales. Cold-blooded. |
| Aves (Birds) | 4-Chambered | Lungs + Air Sacs | Pneumatic (hollow) bones. Feathers. Warm-blooded. |
| Mammalia | 4-Chambered | Lungs | Mammary glands. Hair on skin. External ear (Pinna). |
📝 Rapid Fire MCQs
Q1. Which of the following animals is not a homeotherm (warm-blooded)?
- A) Camelus
- B) Chelone
- C) Macropus
- D) Psittacula
Click to check Answer
Answer: B) Chelone (Turtle – Reptile, Cold-blooded).
Q2. Malpighian tubules are the excretory organs in:
- A) Arthropods
- B) Platyhelminthes
- C) Annelids
- D) Molluscs
Click to check Answer
Answer: A) Arthropods (Insects like Cockroach).