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🐚 Phylum Mollusca – NEET Notes, Examples, and Tips

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📚 Introduction

Phylum Mollusca is another important phylum for NEET, comprising soft-bodied animals that often have a hard shell. Mollusks include familiar organisms like snails, clams, and octopuses. This phylum is diverse in form and function, with species that thrive in both aquatic and terrestrial habitats.

In this blog, we will cover the essential features of mollusks, their classification, and examples you need to know for NEET.

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🧬 Key Features of Mollusca

Feature	Details
Symmetry	Bilateral symmetry
Germ Layers	Triploblastic (three layers)
Body Cavity	Coelomate (true body cavity)
Body Structure	Soft body, often with a calcareous shell
Locomotion	Muscular foot for movement
Digestive System	Complete digestive system (mouth to anus)
Respiratory System	Gills (aquatic), lungs (terrestrial)
Circulatory System	Open circulatory system (except in cephalopods)
Nervous System	Simple, ganglia present
Reproduction	Sexual (dioecious or hermaphroditic)
Habitat	Aquatic, terrestrial

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🔬 Types of Mollusca – Focus on Common Examples

1. Gastropoda (e.g., Snails, Slugs) – The largest and most diverse class of mollusks. They have a spirally coiled shell or are shell-less (like slugs).

2. Bivalvia (e.g., Clams, Mussels) – These mollusks have a two-valved shell and are filter feeders. They play an important role in water filtration.

3. Cephalopoda (e.g., Octopuses, Squids) – Known for their high intelligence, cephalopods have well-developed nervous systems, tentacles, and jet propulsion for movement.

4. Polyplacophora (e.g., Chitons) – These marine mollusks have eight dorsal plates and are found clinging to rocks in intertidal zones.

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⚡ Unique Features of Mollusca

• Soft Body: Mollusks have a soft body that is typically covered by a calcareous shell (in most species).

• Mantle: The mantle is a unique structure in mollusks that secretes the shell and helps in respiration and excretion.

• Radula: Mollusks like gastropods use a specialized feeding organ called the radula, a toothed structure that scrapes food from surfaces.

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🧠 Smart Mnemonic

“Mollusks Move Softly, Shells Sealed, Many Vary.”

• Mollusks – Refers to the phylum

• Move Softly – Soft-bodied organisms

• Shells Sealed – Calcareous shells in many species

• Many Vary – Diverse classes: Gastropoda, Bivalvia, Cephalopoda

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🔬 Structure of a Mollusk (e.g., Clam)

The clam is a classic example of a bivalve mollusk, and here’s how it is structured:

• Body: The body is bilaterally symmetrical and divided into two parts: the head-foot (for movement) and the visceral mass (containing internal organs).

• Shell: The shell is composed of two valves and is secreted by the mantle.

• Mantle: The mantle surrounds the body and is involved in secretion, respiration, and excretion.

• Digestive System: Includes mouth, radula (in some), intestine, and anus.

• Respiratory System: Aquatic mollusks like clams have gills for oxygen exchange.

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🎯 NEET PYQ Alerts – Mollusca

1. What is the main function of the mantle in mollusks?
   ✅ Answer: Secretion of the shell and respiration

2. Which of the following mollusks has a closed circulatory system?
   ✅ Answer: Cephalopods (e.g., Octopus)

3. What type of shell does a clam have?
   ✅ Answer: Two-valved shell (bivalve)

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🧾 Summary Table

Feature	Mollusca
Symmetry	Bilateral
Germ Layers	Triploblastic
Body Cavity	Coelomate
Body Structure	Soft body, often with a calcareous shell
Locomotion	Muscular foot
Respiratory System	Gills (aquatic), lungs (terrestrial)
Digestive System	Complete (mouth to anus)
Nervous System	Simple, ganglia
Circulatory System	Open (except in cephalopods)
Reproduction	Sexual (dioecious or hermaphroditic)
Habitat	Aquatic, terrestrial

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🔗 Stay Connected with Our NEET Bio Blogs:

• 📘 biologyatease1.blogspot.com – NEET Notes & Diagrams

• 🎯 neetpyqall.blogspot.com – NEET PYQs Solved Smartly

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📝 Conclusion

Phylum Mollusca is a diverse and fascinating group of organisms, ranging from snails with their coiled shells to the intelligent octopus. Mollusks play essential roles in various ecosystems and exhibit unique features like the mantle, radula, and calcareous shells. For NEET, make sure you understand these features, their roles in ecosystems, and how different mollusks are adapted to their environments.

👉 Up next: Phylum Echinodermata – The Spiny-skinned Organisms!

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