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Section 3: Mollusks
Mollusks are coelomates with a muscular foot, a mantle, and a
digestive tract with two openings.
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What I Know
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What I Want to Find Out
L
What I Learned
Essential Questions
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What is the importance of the coelom to mollusks?
What is the function of the mantle and what are its adaptive advantages to
mollusks?
What is the importance of mucus and the muscular foot to mollusks?
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Mollusks
Vocabulary
Review
New
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herbivore
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mantle
radula
gill
open circulatory system
closed circulatory system
nephridium
siphon
Mollusks
Body Structure
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Part of phylum Mollusca, include slugs, snails, scallops, and squid.
May be the first coelomates
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Mollusks
Body Structure
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Have bilateral symmetry, a soft internal body, a digestive tract with two
openings, a muscular foot, and a mantle – a membrane that surrounds the
internal organs
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Mollusks
Body Structure
Feeding and digestion
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Many mollusks use a radula, a
tonguelike organ with rows of teeth, to
scrape food into their mouths.
Other mollusks, such as clams, filter
feed and do not have radulas.
Have a complete gut with digestive
glands, stomach, and intestines
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Mollusks
Body Structure
Respiration
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Most mollusks have gills, respiratory structures that consist of filamentous
projections with lots of surface area for gas exchange.
Land snails and slugs remove oxygen from the air using the lining of their
mantle cavities.
Gills also function in filter feeding.
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Mollusks
Body Structure
Circulation
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Most mollusks have an open circulatory system, where blood is pumped
out of vessels into open spaces surrounding the body organs.
Some mollusks have a closed circulatory system, where blood is confined
to vessels as it moves through the body.
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Mollusks
Body Structure
Excretion
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Mollusks get rid of metabolic wastes from cellular processes through
structures called nephridia.
After nephridia filter the blood, waste is passed out through the mantle
cavity.
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Mollusks
Body Structure
Response to stimuli
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Mollusks have a nervous system that coordinates movement and
behavior.
More highly evolved mollusks, such as octopuses, have brains.
Most mollusks have simple eyes.
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Mollusks
Visualizing Movement in Mollusks
Animation
FPO
Add link to animation from page 740 (Figure 17) here.
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Mollusks
Body Structure
Movement
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Mollusks with two shells can clap their shells together for rapid bursts of
swimming.
Snails and slugs move along a trail of mucus produced by their muscular
foot.
Octopuses and squids take water into the mantle cavity and expel it
through a tube called a siphon.
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Mollusks
Body Structure
Reproduction
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Mollusks reproduce sexually.
All mollusks share similar developmental patterns.
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Mollusks
Diversity of Mollusks
Gastropods
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Gastropoda, or stomach-footed, is the largest class of mollusks.
Most species of gastropods have a single shell, such as snails and
limpets.
Other gastropods have no shell, such as slugs and nudibranchs.
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Mollusks
Diversity of Mollusks
Bivalves
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Bivalves are two-shelled mollusks, such as clams and oysters.
All aquatic, most marine
Filter-feeders
Burrow or attach to hard surfaces such as rocks
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Mollusks
Diversity of Mollusks
Cephalopods
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Cephalopods are the head-footed mollusks, such as octopuses and
squid.
Most cephalopods have an internal shell, with the exception of the
chambered nautilus.
The cephalopod foot is divided into arms and tentacles with suckers.
Octopuses are considered to be the most intelligent mollusk, are capable
of complex learning
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Mollusks
Ecology of Mollusks
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Important to marine and terrestrial food webs as predators, herbivores,
scavengers, and filter feeders
Can be keystone species, a species who’s health influences the health of
the entire ecosystem
• Filter feeders are important for cleaning aquatic ecosystems
• Filter feeders can also serve as environmental monitors as they
accumulate toxins in their tissues
• Some snails produce toxins with pharmaceutical promise
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Mollusks
Review
Essential Questions
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What is the importance of the coelom to mollusks?
What is the function of the mantle and what are its adaptive advantages to
mollusks?
What is the importance of mucus and the muscular foot to mollusks?
Vocabulary
• mantle
• radula
• gill
Copyright © McGraw-Hill Education
• open circulatory system
• closed circulatory system
• nephridium
• siphon
Mollusks