MOLLUSKS:MOLLUSKS:

• Slugs, snails, and animal that once Slugs, snails, and animal that once lived in shells in the ocean or on the lived in shells in the ocean or on the beach.beach.

• Phylum MolluscaPhylum Mollusca

• Range from slow-moving slug to jet-Range from slow-moving slug to jet-propelled squidpropelled squid

• Found in oceans, freshwater and Found in oceans, freshwater and moist terrestrial habitatsmoist terrestrial habitats

• Oysters and mussels live firmly Oysters and mussels live firmly attached to the ocean floor or to the attached to the ocean floor or to the bases of docks or wooden boats.bases of docks or wooden boats.

• Squid and the octopus swim freelySquid and the octopus swim freely

• Slugs and snail crawl slowly over the Slugs and snail crawl slowly over the forest floor.forest floor.

• 100 000 species100 000 species• Some have shells Some have shells • Bilateral symmetryBilateral symmetry• True coelomTrue coelom• Two body openingsTwo body openings• Muscular “foot” for movementMuscular “foot” for movement• Mantle: thin membrane that surrounds Mantle: thin membrane that surrounds

the internal organs of the molluskthe internal organs of the mollusk• In mollusks with shells, the mantle In mollusks with shells, the mantle

secretes the shell.secretes the shell.

How mollusks obtain food:How mollusks obtain food:

• Radula: located within the mouth of a Radula: located within the mouth of a mollusk, is a tongue-like organ with rows mollusk, is a tongue-like organ with rows of teeth.of teeth.

• The radula is used to drill, scrape, grate or The radula is used to drill, scrape, grate or cut food. cut food.

• Some mollusks are grazers, some are Some mollusks are grazers, some are predators, and some are filter feeders.predators, and some are filter feeders.

• Bivalves do not have radulas, they are Bivalves do not have radulas, they are filter feeders. filter feeders.

Reproduction in Mollusks:Reproduction in Mollusks:

• Most have separate sexes and reproduce Most have separate sexes and reproduce sexually.sexually.

• Eggs and sperm are released at the same Eggs and sperm are released at the same time into the water where external time into the water where external fertilization takes place.fertilization takes place.

• Many gastropods are hermaphrodites.Many gastropods are hermaphrodites.• Having the same individual produce both Having the same individual produce both

sperm and eggs increases the likelihood of sperm and eggs increases the likelihood of fertilization in slow-moving animals.fertilization in slow-moving animals.

Nervous Control in Mollusks:Nervous Control in Mollusks:

• Simple nervous system with a brain Simple nervous system with a brain and associated nerves that and associated nerves that coordinate movement and behavior.coordinate movement and behavior.

• Paired eyes that range from simple Paired eyes that range from simple cups that detect light to complex cups that detect light to complex eyes in the octopus that have irises, eyes in the octopus that have irises, pupils and retinas and function as pupils and retinas and function as well as the human eye.well as the human eye.

Circulation in Mollusks:Circulation in Mollusks:

• Well-developed circulatory system Well-developed circulatory system with a three-chambered heart.with a three-chambered heart.

• Open circulatory: blood is pumped Open circulatory: blood is pumped through vessels and into open spaces through vessels and into open spaces surrounding organs.surrounding organs.

• This exposes organs directly to blood This exposes organs directly to blood containing oxygen and nutrients and containing oxygen and nutrients and easily removes wastes.easily removes wastes.

• Some mollusks (such as the octopus) Some mollusks (such as the octopus) has a closed circulatory system.has a closed circulatory system.

• Closed circulatory system: blood Closed circulatory system: blood moves through the body enclosed in moves through the body enclosed in a series of vesselsa series of vessels

Respiration in Mollusks:Respiration in Mollusks:

• Most mollusks have respiratory Most mollusks have respiratory structures called gills.structures called gills.

• Gills increase the surface area Gills increase the surface area through which gases can diffuse. through which gases can diffuse. They are an extension of the mantle.They are an extension of the mantle.

• In land snails and slugs, the mantle In land snails and slugs, the mantle has evolved into a primitive lung.has evolved into a primitive lung.

Excretion in Mollusks:Excretion in Mollusks:

• Oldest known animals to have evolved Oldest known animals to have evolved excretory structures called nephridiaexcretory structures called nephridia

• Nephridia: organs that remove metabolic Nephridia: organs that remove metabolic wastes from an animal’s body.wastes from an animal’s body.

• Mollusks have one or two nephridia that Mollusks have one or two nephridia that collect wastes from the coelom.collect wastes from the coelom.

• Wastes are discharged into the mantle Wastes are discharged into the mantle cavity, and expelled from the body by the cavity, and expelled from the body by the pumping of the gills. pumping of the gills.

Diversity of Mollusks:Diversity of Mollusks:• Seven classesSeven classes

• These are the improtant 3These are the improtant 3– GastropodaGastropoda– BivalviaBivalvia– CephalopodaCephalopoda

Gastropods:Gastropods:

• One-shelled mollusksOne-shelled mollusks• Largest classLargest class• Stomach-footed (named for the way Stomach-footed (named for the way

that the large foot is positioned under that the large foot is positioned under the body)the body)

• Slugs have not shellSlugs have not shell• Snails, abalones, conches, periwinkles, Snails, abalones, conches, periwinkles,

whelks, limpets, cowries and coneswhelks, limpets, cowries and cones

• May be found in freshwater, May be found in freshwater, saltwater, or moist terrestrial saltwater, or moist terrestrial environments.environments.

• May be plant eaters, predators or May be plant eaters, predators or parasites.parasites.

Slugs:Slugs:

• No shellNo shell• Body is protected by a thick layer of Body is protected by a thick layer of

mucus.mucus.• Nudibranchs: colorful sea slugsNudibranchs: colorful sea slugs• Nudibranchs feed on jellyfish and Nudibranchs feed on jellyfish and

incorporate their nematocysts into incorporate their nematocysts into their own bodies which are expelled their own bodies which are expelled whenever a predator tries to feed on whenever a predator tries to feed on the slug.the slug.

Bivalves:Bivalves:

• Two-shelled mollusksTwo-shelled mollusks• Clams, oysters and scallopsClams, oysters and scallops• Most are marine, but a few a Most are marine, but a few a

freshwater.freshwater.• Range in size from 1 mm to 1.5 metersRange in size from 1 mm to 1.5 meters• No distinct head or radulaNo distinct head or radula• Most use their muscular foot for Most use their muscular foot for

burrowing in the mud or sand at the burrowing in the mud or sand at the bottom of the ocean or lake.bottom of the ocean or lake.

• A ligament like a hinge connects the two A ligament like a hinge connects the two shells.shells.

• Filter feedersFilter feeders

• Cilia beat to draw water into an incurrent Cilia beat to draw water into an incurrent siphon.siphon.

• As water moves over the gills, food and As water moves over the gills, food and sediment are trapped in mucus. Cilia that sediment are trapped in mucus. Cilia that line the gills push the food particles into line the gills push the food particles into the stomach.the stomach.

• The cilia also act as a sorting device.The cilia also act as a sorting device.

• Any rejected material is transported Any rejected material is transported to the mantle where it is expelled to the mantle where it is expelled through the excurrent siphon.through the excurrent siphon.

Cephalopods:Cephalopods:

• Head-footed mollusksHead-footed mollusks

• All marineAll marine

• Octopus, squid, cuttlefish, and Octopus, squid, cuttlefish, and chambered nautiluschambered nautilus

• The only cephalopod with a shell is the The only cephalopod with a shell is the chambered nautilus.chambered nautilus.

• The cuttlefish has a reduced internal The cuttlefish has a reduced internal shell.shell.

• Very complex structuresVery complex structures

• Predators that swim or walk over the Predators that swim or walk over the ocean floor pursuing their prey.ocean floor pursuing their prey.

• They grab prey with their tentacles.They grab prey with their tentacles.

• The foot has evolved into structures The foot has evolved into structures with hooks, suckers or adhesive with hooks, suckers or adhesive structures.structures.

• The tentacles bring the prey to the The tentacles bring the prey to the mouth where it is bitten by the beak-mouth where it is bitten by the beak-like jaw.like jaw.

• The food is then pulled into the The food is then pulled into the mouth by the radula.mouth by the radula.

• Possess siphons that expel water.Possess siphons that expel water.• By expelling water forcefully, these By expelling water forcefully, these

mollusks can move quickly by jet mollusks can move quickly by jet propulsion.propulsion.

• Squids can attain speeds of 20 Squids can attain speeds of 20 meters per second with this method.meters per second with this method.

• They also expel “ink” to confuse and They also expel “ink” to confuse and escape predators.escape predators.