There are over 50,000 known species of mollusks, which include snails, clams, mussels, squid, and octopuses. Mollusks generally have a soft body with 3 regions - a head, visceral mass containing organs, and a muscular foot. They usually have a hard shell secreted by the mantle, and use a rasping radula and gills to feed and breathe. The three main types of mollusks are univalves with one shell, bivalves with two shells, and cephalopods like squid and octopuses. Univalves specifically refer to gastropods like snails that have a single coiled shell and retractable foot and head

1. MOLLUSKS AND
UNIVALVES
BY VANCE JARRETT SANTOS
GRADE 5 SIMON

2. MOLLUSKS
There are over 50,000 known species of Mollusks, which
makes them second only to the Arthropods in invertebrate
phylum size.
Among the Mollusks are some of the most well known of
invertebrate sea creatures, like snails, clams, mussels, squid,
and octopods.
Mollusks are other animals with soft bodies.
They live in the ocean, streams, ponds, and even in moist
soil.

3. MOLLUSKS have 3 BODY REGIONS
In general, mollusks have 3 body regions: a head, a visceral
mass, and a "foot."
HEAD - contains the sense organs and "brain“
VISCERAL MASS - contains the internal organs
“FOOT" - is the muscular lower part of the body which is in
contact with the substrate
Mollusks usually have a shell (although some do not).
Mollusks also have an extension of the body wall called the
MANTLE. This portion of the animal's anatomy is responsible
for secreting the shell. The mantle encloses the mantle cavity
which contains the Ctenidia (gills), anus and excretory pores.

4. MORE FUN FACTS
ABOUT MOLLUSKS
Many mollusks have a radula, a
tongue of sorts, which is rough like
sandpaper and is used to rasp away
at food. The radula is made of a
hard material called chitin, the
same material of which Arthropod
exoskeletons are made.
In addition, some Mollusk radulae
are impregnated with magnetite to
give them superior wear
characteristics.

5. MORE FUN FACTS
ABOUT MOLLUSKS
Mollusks have a digestive system
with two openings and a circulatory
system.
They have gills, a special organ they
use for absorbing oxygen from
water.
They have hard body coverings
called shells that can be single,
double or composed of several
parts.

6. THREE TYPES
OF MOLLUSKS
1. UNIVALVE OR
GASTROPODS
2. BIVALVES
3. CEPHALOPODS

7. UNIVALVE OR
GASTROPOD
Univalves are as the name suggests –
‘one’ shell or a shell having one piece.
are also known as gastropods.
A mollusk with a univalve shell
and head that live inside the shell and
or retract outside or inside the shell.
live in the water or outside the water.
Examples of univalves include
abalone, and conchs.

8. MORE FUN FACTS ABOUT
THE UNIVALVE
The snail is a univalve mollusks
that has one shell. It has a
muscular foot along the ventral
side of the body for crawling.
Its foot releases slime where it
glides. The body is covered with
hard shell that protects it from its
enemies.

9. HOW DO UNIVALVES
GROW?
Gastropods lay eggs. The eggs of some
species contain a large yolk.
Development of the eggs may be within
the body, or the eggs may be expelled to
develop externally. Eggs develop into
larvae.
Those species that will develop a shell
start it while larvae. As the animal
develops, it adds another curl of shell,
ending in an opening from which the
head and foot of the animal emerge.

10. WHAT DO
THEY EAT?
Gastropods feed on very small
things. Most of them scrape or brush
particles from surfaces of rocks,
seaweeds, animals that don't move,
and other objects.
For feeding, gastropods use a
radula, a hard plate that has teeth.
Gastropod feeding habits are
extremely varied, although most
species make use of a radula in
some aspect of their feeding
behavior. Some graze, some browse,
some feed on plankton, some are
scavengers or detritivores, some are
active carnivores.

11. EXAMPLES OF
UNIVALVES
Gastropods or univalves are the largest
class of mollusks. Except for slugs, each has
a single shell. Members of the univalve class
are :
* Snails
* Slugs
* Abalones
* Whelks
* Sea slugs
* Conches

12. PREPARED AND PRESENTED BY :
VANCE JARRETT SANTOS