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