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Mollusks are coelomates with a muscular foot, a mantle, and a digestive tract with two openings.
Section 3: Mollusks
KWhat I Know
WWhat I Want to Find Out
LWhat I Learned
Essential Questions• 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?
MollusksCopyright © McGraw-Hill Education
Review• herbivore
New• mantle• radula• gill• open circulatory system• closed circulatory system• nephridium• siphon
MollusksCopyright © McGraw-Hill Education
Vocabulary
Body Structure• Part of phylum Mollusca, include slugs, snails, scallops, and squid.• May be the first coelomates
MollusksCopyright © McGraw-Hill Education
Body Structure• 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
MollusksCopyright © McGraw-Hill Education
Body Structure
Feeding and digestion• 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
MollusksCopyright © McGraw-Hill Education
Body Structure
Respiration• 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.
MollusksCopyright © McGraw-Hill Education
Body Structure
Circulation• 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.
MollusksCopyright © McGraw-Hill Education
Body Structure
Excretion• 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.
MollusksCopyright © McGraw-Hill Education
Body Structure
Response to stimuli• Mollusks have a nervous system that coordinates movement
and behavior.• More highly evolved mollusks, such as octopuses, have brains.• Most mollusks have simple eyes.
MollusksCopyright © McGraw-Hill Education
Visualizing Movement in Mollusks
Animation
FPOAdd link to animation from page 740 (Figure 17) here.
MollusksCopyright © McGraw-Hill Education
Body Structure
Movement• 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.
MollusksCopyright © McGraw-Hill Education
Body Structure
Reproduction• Mollusks reproduce sexually.• All mollusks share similar developmental patterns.
MollusksCopyright © McGraw-Hill Education
Diversity of Mollusks
Gastropods• 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.
MollusksCopyright © McGraw-Hill Education
Diversity of Mollusks
Bivalves• 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
MollusksCopyright © McGraw-Hill Education
Diversity of Mollusks
Cephalopods• 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
MollusksCopyright © McGraw-Hill Education
Ecology of Mollusks• 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
MollusksCopyright © McGraw-Hill Education
MollusksCopyright © McGraw-Hill Education
Review
Essential Questions• 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
• nephridium• siphon
• open circulatory system
• closed circulatory system