Mollusks   Phylum Mollusca

  Coelomates- have coelom

 More than 110,000 species

  Survive on land, fresh and marine waters.

Body Structure   Bilateral symmetry

  Soft internal body

  Digestive tract, respiratory system, circulatory system and nervous system.

 Have a mantle; which is a membrane that surrounds the internal organs or mollusks.   Mantle can secrete calcium carbonate to form a

shell.

Body structure

Feeding and digestion   Can be herbivorous, carnivorous or filter

feeders.

  Radula- tonguelike organ with rows of teeth.

  Radula is used for scraping algae off rocks or to drill into other animals to feed on internal body parts.

 Have two openings to digestive tract.

 Have stomach and intestine

Respiration  Most mollusks have gills

  Gills- parts of the mantle that consist of a system of filamentous projections.   used to transport oxygen into and to remove

carbon dioxide from the blood.   Move water through the mantle

  Increase surface area for gas diffusion

  Land snails and slugs take in oxygen using mantle cavities.

Circulation   Have a chambered heart

  Most mollusks have a open circulatory system   Blood is pumped to open spaces surrounding body

organs   Utilized by slow moving animals (snails, slugs)

  Some mollusks have closed circulatory system   Blood is confined to vessels as it moves through body   Used by animals that move quickly (squid and

octopus)

Excretion   Most mollusks get rid of metabolic waste through

the nephridia.

  Nephridia- maintains homeostasis in body fluids.

Response to stimuli   Have nervous system that coordinates movement

and behavior.

  Octopus have a brain and a complex eye.

Movement   Muscular foot is used for movement

movement   Squid and octopus use a siphon to move water into

and then expel it out of the mantle.

Reproduction   Reproduce sexually

  Most release eggs and sperm into water at the same time. (external fertilization)

  Hermaphroditic mollusks use internal fertilization.

  All mollusks have a larval stage called a trochophore.

Gastropods (Gastropoda)   Stomach-footed mollusks

  Most have single shell

  Aquatic and moist terrestrial habitats

  Can draw their bodies into their shell when threatened.

  Slugs secrete mucus for protection

  Nudibranchs incorporate jellyfish nematocysts into their bodies after eating them; for protection

  Ex: snails, conches, periwinkles, limpets, cones.

Bivalves (Bivalvia)   Two shelled mollusks

  Most are marine   Few found in freshwater

  Continuously filter feeding

  Ex: clams, mussels, oysters and scallops

Cephalopods (Cephalopoda)   Head-footed mollusks

  Foot is divided into arms and tentacles   Have suckers; used to capture prey

  Most can expel ink when threatened

  Shells:   Nautilus has external shell

  Squid and cuttlefish have internal shell

  Octopus has no shell

  Octopuses, squid and cuttlefish can change color for camouflage

  Nautilus can hide in its shell when threatened.