purpose of delivering a speech varies depending on the occasion or the audience it is delivered to. A wedding speech, for example, is usually delivered to express a congratulatory remark to the newly wed couple or to propose a toast to the audience. In order to ensure a proper delivery of words and ideas, speakers may practice their speaking through speech exercises like tongue twisters.

1. PHYLUM MOLLUSCA
•CLASSIFICATION
•CHARACTERISTICS
•CLASSES
•ECONOMIC IMPORTANCE
•SUMMARY

2. CLASSIFICATION
i. KINGDOM Animalia
ii. PHYLUM Mollusca
iii. CLASS Caudofoveata
iv. ORDER Chaetodermatida
v. FAMILY Chaetodermatidae
vi. GENUS Chaetoderma
vii. SPECIES Chaetoderma Argentum

3. CHARACTERISTICS
• They are mostly found in marine and freshwater. Very few
are terrestrial and found in moist soil.
• They exhibit organ system level of organization.
• Their body has a cavity.
• The body is divided into head, visceral mass, muscular foot
and mantle.
• The head comprises of tentacles and compound eye.
• The body is covered by a calcareous shell.

4. • Mantle cavity functions in excretion ,gas
exchange , elimination of digestive wastes, and
release of reproductive products .
• They have bilateral symmetry .
• Trochophore larvae ,spiral cleavage , and
schizocoelous coelom formation.
• Coelom reduced to cavities sorrounding the
heart , nephridia and gonads .
• Open circulatory system in all but one class
[Cephalopoda].

5. • Radula usually present and used in scraping
food.

6. BODY CAVITY
• The body of mollusc has two main regions the
head –foot and the visceral mass. The head foot
is elongate with an anterior head containing the
mouth and certain nervous and sensory
structures,and an elongate foot, used for
attachment and locomotion . The visceral
mass contains the organ for digestion ,
circulation, reproduction ,and excretion and is
positioned dorsal to the head foot .

7. • The mantle of a mollusc usually attaches to the
visceral mass , enfolds most of the body , and may
secrete a shell that overlies the mantle.The shell of a
mollusc is secreted in three layers .
• The outer layer of shell is called as periotracum.
Mantle cells at the mantle’s outer margin secrete
this protein layer. The middle layer of the shell ,
called the prismatic layer, is the thickest o the three
layers and consist of calcium carbonates mixed with
organic material . Cells at the mantle’s outer layer
margin also secrete this layer . The inner layer of the

8. shell ,the nacreous layer , forms from thin sheets of
calcium carbonate alternating with organic matter.
Cells along the entire epithelial border of the mantle
secrete the nacreous layer. Nacre secretion thickens
the shell .
• Between the mantle and the foot is a space called the
mantle cavity .The mantle cavity opens t the
outside and functions in gas exchange, excretion
elimination of digestive wastes , and release of
reproductive products.

9. • The mouth of the most molluscs possesses a rasping
structure called a radula , which consist of
chitinous belt and rows of posteriorly curved teeth .
The radula overlies a fleshy , tonguelike structure
supported by a cartilaginous odonotophore
.Muscles associated with the odonotophore permit
the radula to be protruded from the mouth.
Muscles assosiated with the radula move the radula
back and forth over the odonotophore . Food is
scraped from a substrate and passed posteriorly to
the digestive tract.

10. CLASSES

11. Examples of classes

12. ECONOMIC IMPORTANCE
• Mollusks are economically important as food,
and their shells are widely used in jewelry and
decorative items.
• There's a good reason why humans have been
eating shellfish like clams and mussels for at
least 165,000 years: these mollusks
are nutritional powerhouses high in
protein, minerals and healthy fats. They're
also great for the health of the oceans too.

13. • In particular, Muricidae produce a suite of
brominated indoles with anti-inflammatory,
anti-cancer and steroidogenic activity, as well as
choline esters with muscle-relaxing and pain
relieving properties. These compounds could
explain some of the traditional uses in wound
healing, stomach pain and menstrual
problems.

14. SUMMARY
• The animals belonging to the phylum Mollusca
have soft-bodies, triploblastic and
bilaterally symmetrical and coelomate.
The study of Mollusca is called Malacology. They
are sluggish invertebrates, with a thin fleshy
envelope or mantle covering the visceral organs.