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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.