DAILY DOSE: SIMPLIFIED LEARNING MATERIAL 2021-22
CLASS: 11th
SUBJECT: BIOLOGY
UNIT No. & NAME: 1 - DIVERSITY OF LIVING ORGANISMS
CHAPTER No. & NAME: 4- ANIMAL KINGDOM
TOPIC: PHYLUM MOLLUSCA
ASSIGNMENT No. 37 DATE: 20.06.2021
INTRODUCTION
PHYLUM MOLLUSCA- The soft bodied animals
(L. Molluscs- soft)
Phylum Mollusca includes soft bodied, unsegmented, eucoelomate animals. These
are called molluscs or shelled animals. Johnston (1650) coined the term ‘Mollusca’.
It is the second largest animal phylum and includes about 85000 species.
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DAILY DOSE: SIMPLIFIED LEARNING MATERIAL 2021-22
ASSIGNMENT No. 37 CLASS: 11th SUBJECT: Biology DATE: 20.06.2021
GENERAL CHARACTERISTICS OF MOLLUSCA:
1 Habitat: They are mostly marine. Many, however, occur in fresh water and
some even in damp soil.
2 Body form: The body of molluscs is unsegmented with a distinct head,
muscular foot and visceral hump. Neopilina is a segmented mollusc.
3 Symmetry: They usually show bilateral symmetry. In some molluscs like
Pila, due to twisting during growth, the adults become asymmetrical.
4 Shell: Shell is secreted by mantle. It is made up of calcium carbonate. Shell
may be external (e.g. most of molluscs), internal (e.g. slug, cuttle fish) or
absent (e.g. Octopus).
5 Mantle (Pallium): It is a thin, fleshy fold of dorsal body wall more or less
covering the body. It encloses a space, which is called mantle cavity.
6 Body Wall: Body wall is single layered epidermis is usually ciliated. Muscles
are unstriped and occur in bundles.
7 Body cavity: The coelom is greatly reduced although they are eucoelomate.
8 Digestive tract: It is complete.
9 Blood vascular system: It is open type. It includes dorsal heart, arteries that
open into sinuses and veins. Blood is blue due to the presence of
haemocyanin.
10 Respiratory organs: These are gills (ctenidia), mantle and pulmonary sac
(in semi terrestrial forms).
11 Excretory organs: These are one or two pairs of sac- like kidneys. Gills are
also excretory in function. Ammonia is the chief excretory material.
12 Skelton: Molluscs generally have shell as exoskeleton.
13 Sense organs: These have eyes, statocyst, and tentacles for equilibrium
and receptors for touch, smell and taste.
14 . Nervous System: Few pairs of ganglia like cerebral visceral and pedal
with nerves are present.
15 . Reproduction: Molluscs reproduce sexually. Sexes are separate and
mostly oviparous. Fertilisation is external or internal.
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DAILY DOSE: SIMPLIFIED LEARNING MATERIAL 2021-22
ASSIGNMENT No. 37 CLASS: 11th SUBJECT: Biology DATE: 20.06.2021
16. Development: They are oviparous. The development is either direct or
indirect (metamorphosis). When the development is indirect it includes
a characteristic larva. Asexual reproduction is absent.
UNIQUE FEATURES OF MOLLUSCANS:
(i) Mantle covers the body,
(ii) Mantle may be surrounded by shell, and
(ii) Nervous system consists of cerebral, visceral, pleural and pedal
ganglia.
ADVANCEMENT OVER ANNELIDS:
(i) Shell is present in many individuals,
(ii) In some forms, a lungs is present for pulmonary respiration, and
(iii) Better developed sense organs such as eyes, statocysts and
osphradia.
CLASSIFICATION OF PHYLUM MOLLUSCA:
Phylum Mollusca are divided into six classes.
Class 1. Monoplacophora (Gk. monas- one, plax- plate, pherein-bearing): The
shell is spoon or cup shaped. They have die characters of both the phylum
Annelida and phylum Mollusca, e.g. Neopilina.
Class 2. Amphineura (Gk. amphi- both + two neuron = nerve): There is a
present non-ganglionated nerve ring around mouth with two pairs of
interconnected nerve cord, e.g. Chaetopleura (Chiton).
Class 3. Scaphopoda (Gk. scapha- boat, podos- foot): Shell is tubular and
open at both ends, e.g. Dentalium.
Class 4. Gastropoda (Gk. gaster- belly, podos- foot): Shell is made up of
one piece. The early embryo is symmetrical but during development the body
twists showing torsion so that the body becomes asymmetrical. It includes
the largest number of molluscs e.g. Pila.
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DAILY DOSE: SIMPLIFIED LEARNING MATERIAL 2021-22
ASSIGNMENT No. 37 CLASS: 11th SUBJECT: Biology DATE: 20.06.2021
Class 5. Pelecypoda (Gk. pelekus- hatchet Podos foot): Shells is made up
of two halves, e.g. Unio.
Class 6. Cephalopoda (Gk. kephale- head, podos- foot): Head and foot
region combined and modified into a structure which has eyes and eight
tentacles, hence the name cephalopod or ‘head foot’ , e.g. Sepia, Octopus.
Examples: Pila (apple snail), Sepia (cuttle fish), Octopus (devil fish).
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DAILY DOSE: SIMPLIFIED LEARNING MATERIAL 2021-22
ASSIGNMENT No. 37 CLASS: 11th SUBJECT: Biology DATE: 20.06.2021
LET US KNOW WHAT WE HAVELEARNT!
PART: A VERY SHORT ANSWER QUESTIONS:-
a) MULTIPLE CHOICE QUESTIONS:-
1) In molluscs, shell is secreted by:
a) mantle b) foot c) head d) visceral hump
2) Pallium encloses a space which is called:
a) muscular foot b) coelom c) mantle cavity d) digestive tract
3) Which of the following is not a mollusc?
a) Pila b) Sepia c) Octopus d) Star fish
4) Phylum mollusc is divided into:
a) six classes b) two classes c) four classes c) five classes
b) TRUE OR FALSE:-
1) Molluscs are soft bodied animals.
2) Molluscua is the largest animal phylum.
c) FILL IN THE BLANKS:-
1) ________ is secreted by mantle.
2) Blood is blue due to the presence of _________.
3) _______ is chief excretory material in moluuscs.
PART:B SHORT ANSWER TYPEQUESTIONS:-
1) What are molluscs? Name any two.
2) Define Pallium. Name various respiratory organs in molluscs.
3) Write unique Features of phylum Mollusca.
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DAILY DOSE: SIMPLIFIED LEARNING MATERIAL 2021-22
ASSIGNMENT No. 37 CLASS: 11th SUBJECT: Biology DATE: 20.06.2021
ANSWER KEY PART A & B
PART- A: VERY SHORT ANSWER TYPE QUESTIONS:
a) MULTIPLE CHOICE QUESTIONS:-
1. a) mantle
2. c) mantle cavity
3. d) Star fish
4. a) six classes
b) TRUE OR FALSE:-
1. True
2. False
c) FILL IN THE BLANKS:-
1. Shell
2. Haemocyanin
3. Ammonia
PART- B SHORT ANSWER TYPE QUESTIONS:-
1) Animals belonging to phylum Mollusca are commonly known as
Molluscs e.g. Pila (apple snail), Sepia (cuttle fish), Octopus (devil fish).
2) Mantle (Pallium) it is a thin, fleshy fold of dorsal body wall more or
less covering the body. It encloses a space, which is called mantle
cavity. Various respiratory organs in molluscs are gills (ctenidia),
mantle and pulmonary sac (in semi terrestrial forms).
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DAILY DOSE: SIMPLIFIED LEARNING MATERIAL 2021-22
ASSIGNMENT No. 37 CLASS: 11th SUBJECT: Biology DATE: 20.06.2021
3) Unique Features of phylum Mollusca are Mantle covers the body,
Mantle may be surrounded by shell, and Nervous system consists of
cerebral, visceral, pleural and pedal ganglia.
PREPARED BY: Iqbal Singh Sandhu, Lecturer in Biology,
GSS Smart School, Dharowali, Gurdaspur, 9872337402
UNDER THE GUIDANCE OF: Sh. Rajan Kumar ,DM-CUM- Principal ,
GSSS, Taragarh,Gurdaspur.9780120956
SUPERVISED BY: Smt. Jasvinder Kaur (Assistant Director)
PPPP Science Sen. Sec. State Coordinator.
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