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MOLLUSKS
Chapter 25.3
Biology
What is a
Mollusk?
• Slugs, snails, squids and
some animals that live in
shells in the ocean or on
the beach.
• Belong to phylum
Mollusca.
• Range from slow moving
slug to the jet-propelled
squid.
What is a
Mollusk?
• Most species live in the
ocean
• Some live in freshwater
• Some live on land
What is a
Mollusk?
• Oysters live firmly
attached to the ocean
floor or to docks and
boats.
• Octopus swim freely in the
ocean.
• Slugs and snails can be
found on the forest floor.
What is a
Mollusk?
• All have bilateral
symmetry
• a coelom
• a digestive tract with two
openings
• A muscular foot
What is a
Mollusk?
• A mantle (membrane that
surrounds the internal
organs
• In shelled mollusks, the
mantle secretes the shell
How do
Mollusks
obtain food?
• Have a radula located
within the mouth.
• It is a tongue-like organ
with rows of teeth.
• It is used to drill, scrape or
cut food
Reproductio
n in
Mollusks
• Reproduce sexually
• Most have separate sexes
• Aquatic = sperm and egg
released into water
• Some are hermaphrodites,
but cannot fertilize
themselves
Nervous
Control in
Mollusks
• Simple nervous system
• Some advanced mollusks
have a brain
• Most have paired eyes that
range from simple cups to
detect light to complex
eyes of an octopus (similar
to humans)
Circulation
in Mollusks
• Have a well-developed
circulatory system
• Some have twochambered hearts (snail)
• Some have threechambered hearts (squid)
Circulation
in Mollusks
• In most mollusks have an
open circulatory system –
blood moves through
vessels into open spaces.
• Some have a closed system
– blood moves through a
body enclosed in a series of
vessels
Respiration
in Mollusks
• Most have gills
• Gills are specialized parts of
the mantle
• Gills increase the surface
area through which gases
can diffuse
Respiration
in Mollusks
• In land snails and slugs,
lungs are present.
• *Lung is more like a gill
than a human lung.
Excretion in
Mollusks
• Have Nephridia.
• Wastes are discharged into
the mantle cavity and
expelled through the gills.
Diversity in
Mollusks
• Phylum Mollusca is large
and diverse.
• Has three classes:
• Gastropoda
• Bivalvia
• Cephalopoda
Gastropods
• Largest class
• Name comes from the way
the animal’s large foot is
positioned under the rest
of the body.
• Snails, slugs, sea
slugs(nudibranches)
Bivalves
• Two-shelled mollusks
• Clams, oysters
• Most are marine, some
freshwater
• Vary in size = 1mm in
length to 1.5 M.
Bivalves
• Have no distinct head or
radula.
• Filter food from water
• Have an incurrent siphon
and in excurrent siphon
Cephalopods
• Head-footed
• Class Cephalopoda
• Includes octopus, and squid
• Most complex of all
mollusks