Phylum Cnidaria – Class 11 NEET Notes | Simple & Smart Tricks

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🐙 Phylum Cnidaria – Class 11 NEET Notes | Simple & Smart Tricks

📚 Introduction

Cnidaria, home to the famous jellyfish, corals, and hydras, is another NEET favorite. With its unique features like stinging cells (nematocysts), this phylum packs a punch in both biology concepts and NEET exams.

Let’s break it down, one sting at a time! ⚡

🌊 Key Features of Cnidaria

Feature Details
Symmetry Radial symmetry
Germ Layers Diploblastic (two layers)
Body Cavity Acoelomate (No coelom)
Locomotion Mostly free-swimming or sessile (hydras)
Digestion Extracellular (gastrovascular cavity)
Nerve System Nerve net (primitive)
Reproduction Asexual (budding) and sexual (gonads)
Special Features Nematocysts (stinging cells)
Habitat Mostly marine, some freshwater (Hydra)

🌸 Unique Structure: Polyp and Medusa Forms

Cnidarians have two basic body forms:

  1. Polyp (sessile)

  2. Medusa (free-swimming)

Example:

  • Polyp: Hydra, Coral

  • Medusa: Jellyfish

🔑 Tip: Medusa = Free-swimming, Polyp = Sessile (stuck on a surface)

⚡ Nematocysts – The Stinging Cells

The nematocysts are the special stinging cells of cnidarians, used for defense and capturing prey.

🧠 Trick: Nema = Needle! Think of the needle that injects toxins!

🧠 Smart Mnemonic

“Cnidarians Can Never Forget Polyp Medusa.”

  • C – Cnidaria

  • N – Nematocysts (stinging cells)

  • F – Freshwater (Hydra)

  • P – Polyp

  • M – Medusa

🔬 Important Examples

  • Hydra (Freshwater)

  • Aurelia (Jellyfish)

  • Adamsia (Sea anemone)

  • Corals (Marine)

🏝️ Tip: Hydra = Freshwater, Aurelia = Marine jellyfish!

📸 Simple Structure Diagram of Hydra

           Tentacles (with nematocysts)
                  ↑
                Mouth
                  ↓
          Gastrovascular Cavity
             (Digestive Cavity)

🎯 NEET PYQ Alerts – Cnidaria

  1. Which animal is an example of the Medusa body form?
    ✅ Answer: Jellyfish (Aurelia)

  2. Which of the following has radial symmetry?
    ✅ Answer: Cnidaria

  3. Stinging cells are found in?
    ✅ Answer: Cnidarians (Nematocysts)

🧾 Summary Table

Feature Cnidaria
Symmetry Radial symmetry
Body Forms Polyp & Medusa
Nematocysts Present
Habitat Marine (except Hydra - freshwater)
Reproduction Asexual (budding) & Sexual
Example Hydra (Polyp), Aurelia (Medusa)

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📝 Conclusion

Cnidaria is easy to understand if you focus on the stinging cells and the two body forms — polyp and medusa. With this simple breakdown, you'll be able to tackle any tricky NEET question.

📌 Keep revising those mnemonics and quick diagrams. These little tricks make all the difference in exam day performance.

👉 Coming up next: Phylum Platyhelminthes – Notes + NEET PYQs


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