Phylum Mollusca: Detailed Notes and MCQs

Introduction

The phylum Mollusca is the second-largest animal phylum (Kingdom Animalia). Molluscs can be found in both terrestrial and aquatic environments, including marine and freshwater habitats. They exhibit an organ-system level of organization and display bilateral symmetry, making them coelomate and triploblastic animals.

Key Characteristics

• Habitat: Terrestrial or aquatic (marine and freshwater)
• Body Organization: Organ-system level
• Symmetry: Bilateral
• Layers: Triploblastic
• Body Cavity: Coelomate
• Body Covering: Calcareous shell
• Segmentation: Unsegmented
• Body Parts: Distinct head, muscular foot, visceral hump

Body Structure

• Head: Contains sensory tentacles
• Foot: Muscular and used for locomotion
• Visceral Hump: Contains the internal organs
• Mantle: Soft, spongy layer of skin covering the visceral hump
• Mantle Cavity: Space between the visceral hump and mantle, housing feather-like gills for respiration and excretion

Feeding and Respiration

• Radula: File-like rasping organ in the mouth used for feeding
• Respiratory System: Feather-like gills present in the mantle cavity

Reproduction

• Dioecious: Separate sexes
• Reproduction: Mostly oviparous with indirect development

Examples

• Pila (Apple snail)
• Pinctada (Pearl oyster)
• Sepia (Cuttlefish)
• Loligo (Squid)
• Octopus (Devil fish)
• Aplysia (Sea-hare)
• Dentalium (Tusk shell)
• Chaetopleura (Chiton)

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FAQs

1. What habitats do molluscs occupy?
   Molluscs are found in terrestrial and aquatic environments, including both marine and freshwater habitats.

2. What kind of body symmetry do molluscs exhibit?
   Molluscs exhibit bilateral symmetry.

3. What are the main body parts of a mollusc?
   The main body parts of a mollusc are the head, muscular foot, and visceral hump.

4. What is the function of the radula in molluscs?
   The radula is a file-like rasping organ used for feeding.

5. How do molluscs respire?
   Molluscs respire through feather-like gills located in the mantle cavity.

6. Are molluscs dioecious or monoecious?
   Molluscs are usually dioecious, meaning they have separate sexes.

7. What type of development do molluscs undergo?
   Molluscs are typically oviparous with indirect development.

8. What is the mantle in molluscs?
   The mantle is a soft and spongy layer of skin that covers the visceral hump.

9. How is the body of molluscs covered?
   The body of molluscs is covered by a calcareous shell.

10. Can you name some examples of molluscs?
    Examples of molluscs include Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), and Octopus (Devil fish).

Multiple-Choice Questions (MCQs)

1. What type of body symmetry do molluscs exhibit?

   a) Radial
   b) Bilateral
   c) Asymmetrical
   d) None of the above

2. Which organ in molluscs is used for feeding?

   a) Mantle
   b) Radula
   c) Gills
   d) Foot

3. Molluscs are usually:

   a) Monoecious
   b) Dioecious
   c) Hermaphrodites
   d) None of the above

4. What type of circulatory system do molluscs have?

   a) Open
   b) Closed
   c) Both a and b
   d) None of the above

5. Which of the following is an example of a mollusc?

   a) Pila
   b) Anopheles
   c) Limulus
   d) Laccifer

6. Where are the feather-like gills of molluscs located?

   a) In the head
   b) In the mantle cavity
   c) In the foot
   d) In the radula

7. What type of development do molluscs undergo?

   a) Direct
   b) Indirect
   c) Both a and b
   d) None of the above

8. Which body part of molluscs contains sensory tentacles?

   a) Foot
   b) Visceral hump
   c) Head
   d) Mantle

9. How is the body of molluscs covered?

   a) Chitinous exoskeleton
   b) Calcareous shell
   c) Feathers
   d) Scales

10. What is the function of the mantle in molluscs?

    a) Feeding
    b) Respiration
    c) Protection
    d) Excretion

Answers to MCQs

1. b) Bilateral
2. b) Radula
3. b) Dioecious
4. a) Open
5. a) Pila
6. b) In the mantle cavity
7. b) Indirect
8. c) Head
9. b) Calcareous shell
10. c) Protection

Also Read:

• NOTES: Class 11
• MCQs: Class 11