Phylum Mollusca: Characteristics, Examples & NEET MCQs | Animal Kingdom Class 11

By Pavan Chaturvedi

  

Welcome to Chaubey Biology Hub, your premier destination for high-quality, NCERT-aligned medical entrance preparation. We take pride in delivering content that doesn't just mirror textbooks but decodes them. This guide on Phylum Mollusca: Characteristics, Examples & NEET MCQs | Animal Kingdom Class 11 is meticulously crafted to meet the rigorous standards of the NTA NEET-UG syllabus, focusing exclusively on the core concepts that matter most."

Before diving into the Phylum Mollusca: Characteristics, Examples & NEET MCQs | Animal Kingdom Class 11 ensure you have gone through comprehensive guide on Phylum Arthropoda: Class 11 Biology One Shot Notes for NEET

 

Table of Contents  

1. ​Introduction: Phylum Mollusca 
2. ​General Features: Organization, Symmetry And  Coelom.
3. ​Body Structure: Head, Muscular Foot aur Visceral Hump 
4. ​The Mantle: Mantle Cavity and  Gills (Ctenidia)  functions.
5. ​Radula: NEET important "Rasping Organ".
6. ​Examples & Tricks
7. ​NEET MCQ Challenge: 100% Questions yahi se aayenge!

Introduction: Phylum Mollusca

• Molluscs  are  soft body animals with unsegmented bodies bodies with calcareous shell. 
• This is the second largest phylum of Animals after the arthropods
• These are primarily aquatic (marine or freshwater) and occasionally terrestrial animals. The study of molluscs is known as Malacology, while the study of their shells is called Conchology.
• ​Evolutionarily, they are characterized as triploblastic, coelomate, and bilaterally symmetrical organisms. 
• However, a unique feature of many molluscs (like Pila) is Torsion, which can make adults asymmetrical. Their most distinctive advancement is a soft, unsegmented body protected by a calcareous shell, and a specialized membrane called the Mantle. 
• From the common garden snail to the giant squid, Mollusca showcases an incredible range of biological diversity and adaptation.

💡 Quick Navigation: Back to [NEET Biology Full Course Hub] for more Unit-wise Study Material."

General Features: Organization, Symmetry aur Coelom.

• They are terrestrial and also found in fresh and marine water.
• They  have an organ-system level of organisation. 
• They are bilaterally symmetrical, triploblastic and coelomate animals. 
• Body is covered by a calcareous shell. with unsegmented body.
• Saxes are separate and development is indirect. 
• Mostly they are oviparous, they lay eggs.
• The anterior head region has sensory tentacles

Body Structure: Head, Muscular Foot aur Visceral Hump 

• Body is divided into with a distinct head, muscular foot and visceral hump. 
• A soft and spongy layer of skin forms a mantle over the visceral hump. 
• Head is  The anterior part of the body which contains sensory organs. In many species, it features tentacles and eyes. It also houses the Radula, a unique rasping organ used for feeding.
• ​Muscular Foot is  A ventral, highly muscular structure primarily used for locomotion (crawling or swimming). Its shape varies across classes—for example, it is a broad sole in snails and modified into tentacles in squids.
• ​Visceral Hump (Visceral Mass ) is the dorsal part of the body that contains most of the internal organs (digestive, excretory, and reproductive systems). It is covered by a soft, spongy layer of skin called the Mantle.

Comparison table between Head Muscular foot and Visceral hump.

Body Part	Description	Main Function
Head	Front part with sensory tentacles.	Sensing the environment.
Muscular Foot	Ventral muscular structure.	Locomotion (Movement).
Visceral Hump	Soft hump containing internal organs.	Digestion, Excretion, Reproduction.

The Mantle: Mantle Cavity and  Gills (Ctenidia)  functions.

• The Mantle is a soft, spongy layer of skin that covers the visceral hump. 
• The space between the visceral hump and the mantle is known as the Mantle Cavity.
•  This cavity plays a crucial role in the survival of molluscs by housing the respiratory and excretory organs.

💡 Related study to understand the Phylum Coelentrata : Phylum Coelenterata (Cnidaria): General Characteristics, Classification & Examples | Class 11 Biology

Functions of Mantle Cavity and Ctenidia (Gills):

• ​The mantle cavity contains feather-like gills called Ctenidia which are respiratory in function.  These gills are richly supplied with blood vessels and facilitate the exchange of gases (oxygen and carbon dioxide) in aquatic molluscs.
• ​Besides respiration, the Ctenidia also perform an excretory function, helping the animal remove nitrogenous waste from the body.

💡​​NEET TIP.

📝  Gills in Mollusca are both Respiratory and Excretory in function.

• ​In some species, the mantle cavity houses sensory organs (like Osphradium) to test the chemical nature of the incoming water.
• ​Shell Secretion: The Mantle itself is responsible for secreting the calcareous shell that protects the soft body of the mollusc.

Radula: NEET important "Rasping Organ

• The mouth contains a file-like rasping organ for feeding, called radula.
• ​It consists of a chitinous ribbon equipped with multiple transverse rows of tiny, curved teeth that act like a saw to scrap or cut food.
• ​ It is primarily used to scrape algae off rocks or to tear food into smaller pieces before swallowing, making it a vital digestive tool.

🔼  Video Highlights & Timestamps

Click the time to jump to that part in the video:

• 00:00 — Introduction to Phylum Mollusca
• 01:02 — General Features (Coelom & Symmetry)
• 03:07 — Body Parts: Head, Foot & Visceral Hump
• 06:02 — What is Mantle?
• 07:17 — Mantle Cavity & Gills (Respiration)
• 08:25 — Radula: The Rasping Organ
• 09:44 — Important Examples (Pila, Octopus, etc.)

💡 Tip: Watching the video while reading notes helps in 100% retention!

Examples of Mollusca  

Octopus

• It is commonly called as Devil fish.
• Body of octopus is divided into head and Visceral hump.
• Octopus is Di branchiate having two gill , two auricle and two kidney.
• Nervous system is well developed.
• Head contain eyes, siphon and eight long arms and two arms posses suckers for the attachment.
• One of the arms is male is modified into Hectocotylized  arm.

Octopus ( Devil fish )

• Animal can crawl by its arms and swim backwards.
• Visceral mass and mantle cavity are enclosed by mantle.
• Shell and nidamental glands are absent.

💡 Related study to understand the Phylum Porifera : Phylum Porifera (Sponges) NCERT Notes & MCQs for NEET Biology

Sepia

• It is commonly called as cuttle fish.
• Body of sepia is divided into head collar and trunk or Visceral hump.
• Sepia is Dibranchiate having two gill , two auricle and two kidney with luminescent property.
• Nervous system is well developed.
• Head contain ten oral arms. Eight  are long arms with several pedicellate suckers around the Mouth. And  two arms posses pedicellate suckers at the called Hectocotylized arms.

Sepia ( cuttle fish )

Head bear a pair of eye without olfactory crest.
Calcareous shell is well developed and maintain buoyancy.
Ink gland secrete ink during irritation and get protection from predator.
💡 Related study to understand the Phylum Platyhelminthes : General Characters, Classification and Example , Multiple Choice questions: NEET

Loligo

It is commonly called as cuttle fish.
Body of sepia is divided into head collar and trunk or Visceral hump.
Head bear a pair of eye without olfactory crest.
Head contain ten oral arms.out of ten, eight oral arms has four row of pedicellate suckers.  
Remaining two arms has six pairs of pedicellate suckers, used in capturing of prey. These are Hectocotylised arms.

Loligo ( Squids)
In male oral arms are modified into copulatory organ .
Loligo has two ctenidia , two auricle and two kidney.
Calcareous shell is well developed and maintain buoyancy.
Ventral siphon is modification of foot.
Pinctada 
It is commonly called as Pearl Oyster .
Shell valves are unequal. Hinge line is straight and bear ear and wing like process.
Left shell is large ,convex and permanently attached with the rock by byssal thread.
Pinctada ( Pearl oyster)

Right shell is small and thin covers the visceral organ.
A single adductor muscle is present.
Right and left mantle lobe are free.
Shell of animal secrete pearl when any insect create irritation.
🦁 Zoology Shortcut: > Master all Animal Phyla from Porifera to Chordata with our easy-to-remember comparison tables: 👉 Animal Kingdom: High-Yield Module
Pila 
It is commonly called as Apple snail .
Body is covered by thick univalved shell and comprises body whorl , penultimate whorl and apex.
Surface of shell is marked by line of growth.
🎯 NEET Must-Know Points:
1. Radula (The File-like Organ):
"The mouth contains a file-like rasping organ for feeding called Radula."

2. Mantle & Mantle Cavity:
A soft/spongy layer of skin forms the Mantle over the visceral hump. The space between the hump and mantle is the Mantle Cavity.
Gills (Ctenidia): Located in the cavity; used for both Respiration and Excretion.
Shell is spirally coiled round the axis called as columella.
Soft parts are differentiated into head, muscular foot and visceral mass.
Pila ( Apple snail)

Head is located at the upper side with one pair of eyes.
Visceral mass contain internal organs and covered by mantle or pallium.
It has great medicinal and experimental value.

Aplysia 
It is commonly called as Sea hare.
Anterior end has head and neck.
Animal is slug like and anterior head are extended into two tentacular folds.
Aplysia (Sea hare)

Head bear a pair of eye at anterior tentacular folds. Behind the eyes, rhinophores are present as tentacular folds.
Mantle cavity is opened at right side and backward pointing into ctenidium.
Anus is posterior located.
There are a pair large fleshy outgrowth called parapodia help in swimming.
Shell is internal and rudimentary.
Dentalium 
Animal is commonly called as Tusk shell.
Body is covered by arched shell secreted by mantle.
Body of animal has vestigial head which represents by proboscis without eyes.
Mouth is surrounded by leaf  tentacles called captacules which are sensory , prehensile and regenerative.
Ctenidia are absent.
Conical foot is emerged from shell to make burrow in sand.
Dentalium ( Tusk Shell)

Liver , muscle and kidney are seen after removing the shell.
Radula is well developed. Anus is located behind the foot.
Respiration takes place by lining of mantle because gills are absent.

Chiton 
Animal is commonly called as sea mouse.
Body is divided into district head large foot and mantle which form leaf like roof of body.
Head contain ventral mouth and labial palps.
Mouth and anus are located at opposite end of the body.
Eyes and tentacles are absent.
Dorsal side of mantle contains series of  eight  calcareous  overlapping plates.
Chiton ( sea mouse)

Several pairs of bipectinate ctenidia are present on either side of body.
Side of mantle form mantle girdle which contain small calcified Spicules  .
​Mollusca Examples Yaad Karne ki "Bhole Nath" Trick:
Trick: "Pila Apple lekar Pinctada (Pearl) dhundhne Gaya, tabhi Octopus (Devil) ne use Dentalium (Shell) aur Chaetopleura pakda diya."
​Pila – Apple Snail
​Pinctada – Pearl Oyster
​Sepia – Cuttlefish
​Loligo – Squid
​Octopus – Devil fish
​Aplysia – Sea hare
​Dentalium – Tusk shell
​Chaetopleura – Chiton
 
In Next Topic we will take deep dive about the  second largest  phylum in which   soft body animals are included  Phylum Echinodermata: Notes, Examples & NEET MCQs (Class 11 Biology)

🎯 NEET MULTIPLE CHOICE QUESTIONS
🔥 100% CHALLENGE
"Questions yahi se aayega... taiyari jeet ki!"
1. Consider the following sentences and select the number of  correct statements.
1. Mollusca is the second largest phylum of Animals after the arthropods.
2.   Molluscan are  found in  fresh and marine water but some are terrestrial.
3. Body of  Molluscan is covered by a Chitin.
4. Molluscan are Coelomate. 
5. Molluscan  are triploblastic with organ system  level of organisation.
A. Two           B. Three
C. Four           D. Five
Answer : C  

2. Body of Molluscan animal is covered by the 
A. Glucosamine 
B. Chitin 
C. Calcareous ossicles 
D. Calcareous Shell 
Answer : D 

3. Body of Molluscan is divided into 
A. Proboscis, Collar and trunk
B. Head , neck and Trunk
C. Head, Muscular foot and visceral hump.
D. Head. Thorax and abdomen.
Answer : C 
 
4. Visceral hump is covered by the mantle which is 
A. Soft and spiny skin
B. Hard and spiny skin
C. Soft and spongy skin
D. Hard and spongy skin
Answer: C 

5. Which of the following statement is not correct.
A. The space between the hump and the mantle is called the mantle cavity.
B. A soft and spongy layer of skin forms a mantle over the visceral hump. 
C. Gills are only  respiratory in  function in Mollusc.
D. Feather like gills are present inside the mantle cavity.
Answer: C 

6. In Mollusc, Gills are involved in 
A. Respiration only
B. Excretion only
C. Respiration and Excretion
D. Respiration , Excretion and Reproduction 
Answer : C 

7. Gills are enclosed in mantle cavity which is space between 
A. Muscular foot and mantle
B. Visceral hump and mantle
C.Muscular foot and Visceral hump.
D. Calcareous shell and mantle
Answer : B 

8.The mouth of mollusc contains a file-like rasping organ for feeding called A.Radula
B.Muscular pharynx
C.Ctenidia
D.labrum
Answer : A 

9. Consider the following sentences and select the number of  correct statements.
1. Mostly Molluscan are oviparous, they lay eggs.
2. Molluscan have tentacles on anterior head.
3. Saxes are separated in Molluscan. 
4. Development is indirect in Mollusca.
A. Two           B. Three
C. Four           D. One
Answer : C  

10. Which of the following Mollusca is called as Pearl oyster.
A. Pinctada     B. Aplysia
C. Dentalium   D. Chiton
Answer : A 

11. Which of the following pair is  not correctly matched.
A. Aplysia : Sea mouse
B. Dentalium: Tusk shell
C. Pila : Apple Snail
D. Loligo : Squid
Answer : A 

12. Match the list
A. Aplysia   1. Sea hare
B. Octopus 2.Cuttle fish
C. Sepia     3. Devil fish
D. Chiton    4. Sea mouse

     A      B       C      D
A.  1       2       3       4
B.  1       3       2       4
C.  4      3       2        1
D.  4       2       3       1
Answer: B Explanation

13. Identify the animal of Mollusca in given Diagram

A. Unio          B. Pila
C. Pinctada   D. Chiton
Answer : B

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