Mollusks   Coelomates- have coelom  More than 110,000  Survive on land, fresh and marine waters. Body Structure  Bilateral symmetry  Soft internal body  Digestive tract, respiratory system, and .  Have a ; which is a membrane that surrounds the internal organs or mollusks.  Mantle can secrete to form a shell. Body structure Feeding and  Can be herbivorous, carnivorous or filter feeders.  - tonguelike organ with rows of teeth.  Radula is used for scraping algae off rocks or to drill into other to feed on internal body parts.  Have two openings to digestive tract.  Have and intestine Respiration  Most mollusks have  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 and take in oxygen using mantle cavities. Circulation  Have a chambered  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 ( and ) 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 and a complex . Movement  Muscular foot is used for movement movement  Squid and octopus use a to move water into and then expel it out of the mantle. Reproduction  Reproduce sexually  Most release and sperm into water at the same time. (external fertilization)  Hermaphroditic mollusks use internal fertilization.  All mollusks have a larval stage called a . Gastropods ()  Stomach-footed mollusks  Most have single shell  Aquatic and moist terrestrial habitats  Can draw their bodies into their shell when threatened.

 Slugs secrete for protection  Nudibranchs incorporate jellyfish nematocysts into their bodies after eating them; for protection  Ex: snails, , periwinkles, , cones.

Bivalves ()  Two shelled mollusks  Most are marine  Few found in freshwater  Continuously filter feeding  Ex: , , and

Cephalopods (Cephalopoda)  Head-footed mollusks  Foot is divided into arms and  Have suckers; used to capture prey  Most can expel ink when threatened  Shells:  has external shell  Squid and have internal shell  Octopus has no shell  , squid and cuttlefish can change color for camouflage

 Nautilus can hide in its shell when threatened.