The document summarizes key features of the phylum Mollusca. It discusses that Mollusca are soft-bodied marine animals, though some are found in freshwater or land. They have a mantle that secretes an external shell made of calcium carbonate. Their body plan includes a head, visceral mass containing organ systems, and a foot for locomotion. Their digestion is through a complete digestive tract containing a rasping organ called a radula. Respiration occurs through gills or directly through the mantle. Their circulatory system is open with one or more hearts and sinuses. Waste is excreted through one or two pairs of sac-like kidneys. Their nervous system contains three paired

1. ANIMAL KINGDOM
PHYLUM MOLLUSCA

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4. Introduction, Other features, Body wall and parts,
Digestion, Respiration, Circulation, excretion, Nervous
system, Reproduction
Synopsis

5. Introduction

6. INTRODUCTION
◈ It is second largest Phylum.
◈ Mollusca (Soft bodied) are marine. Some are also
found in fresh water or on land.
◈ Johnston coined the name Mollusca.
◈ Study of this phylum is known as Malacology
◈ Study of shell of molluscan is known as Concology.

7. Other features

8. OTHER FEATURES
◈ Body is unsegmented with variety of shapes.
◈ Neopilina is exceptionally segmented.
◈ They are usually bilateral. Few are secondarily
asymmetrical (snail) due to twisting (Torsion) during
growth.
◈ These are triploblastic with organ system level of
organisation.

9. Body wall
Body parts

10. BODY WALL AND PARTS
◈ Body wall includes one layered epidermis (usually
ciliated) with unstriped muscles found in bundles
◈ Body parts consist of
◈ Head with sense organ. Head is absent in Pelecypod
◈ Dorsal visceral mass containing organs system
◈ Ventral foot for locomotion
◈ Thin fleshy fold or outgrowth of dorsal body wall
covers the body. This fold is called mantle or pallim.

12. BODY PART
◈ The mantle usually secretes as a external limy shell
◈ Shell is made up of Calcium carbonate and choncheolin
protein
◈ Shell may also be internal (Cattle fish), reduced and
even absent (Octopus)
◈ Coelom is greatly reduced.
◈ It is presented by cavities in the pericardium kidneys
and gonads. Space among the viscera contain blood and
form haemocoel.

13. Digestion

14. DIGESTION
◈ Digestive tract is
complete. Buccal cavity
contain a rasping organ
the Radula with
transverse row of
teeth.
◈ Anus pens into the
mantle cavity. Digestive
glands are known as
hepatopancreas.

15. Respiration

16. RESPIRATION
◈ Respiration is usually by bills. i.e.
Ctenidia are in the mantle cavity
but respiration may takes pace by
body surface also.
◈ Dentalium respire by Mantle.
◈ Pila respire by pulmonary sac on
land and by gills in water.

17. Circulation

18. CIRCULATION
◈ Circulatory system is open.
◈ It includes dorsal pulsatile heart and a few arteries
that open into sinuses.
◈ Cephalopoda has closed type of circulatory system
◈ Blood has a copper containing, blue respiratory
pigment Haemocyanin.
◈ Blood is colourless with ameobocytes.

19. Excretion

20. EXCRETION
◈ Excretory system includes 1 or 2 pairs of sac like
kidneys, which open into the mantle cavity. Kidney of
molluscans are Metanephridia known as Kaber’s organs
or Organ of Bojanus.
◈ Excretory matter is ammonia or uric acid.

21. Nervous system

22. NERVOUS SYSTEM
◈ Three paired ganglia:
◈ Cerebral (above the mouth)
◈ Pedal (in the foot)
◈ Visceral (in visceral mass)
◈ Sense organs:
◈ Eye - Present over a stalk called ommatophore
◈ Statocyst/Lithocyst - For equilibrium in foot
◈ Osphradia - Chemoreceptor/Olfactory as well as for
testing chemical & physical nature of water.

23. Reproduction

24. REPRODUCTION
◈ Sexes usually separate (snail has ovotestis). Gonads
have ducts.
◈ Fertilization may be external or internal.
◈ Cleavage is spiral, determinate, unequal and
holoblastic.
◈ Development is - Direct or indirect.
◈ Trochophore is very common larva of Mollusca phylum.
Larva Glochidium (Fresh water mussel) and Veliger,
(Pila)

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