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10-1 Mollusks Characteristics invertebrates with soft unsegmented bodies that are often protected by a hard outer shell have a thin layer of tissue called a mantle that covers its internal organs a foot (has different functions, crawling, digging, or catching prey in many mollusks the mantle produces the hard shell body structure bilateral symmetry digestive system with two openings circulatory system most have an open circulatory system (blood is not always inside blood vessels.) the organs are located together so blood can slosh over them and return to the heart Cephalopods have a closed circulatory system Obtaining Oxygen most mollusks that live in water have gills gills organ that remove oxygen from the water to blood CO2 flows out of blood and into water cilia move back and forth making water flow over gills Three classifications of mollusks based on physical characteristics gastropods, bivalves, and cephalopods Gastropo ds (include snail s and slug s) Largest group of mollusks have one external shell or no shell live nearly everywhere on earth obtaining food herbivores (plant eaters) or carnivores (meat eaters) radual a flexible ribbon of tiny teeth herbivores use them like sandpaper to tear into plant tissue carnivores use differently (oyster drill uses it to drill through shells and scrap up the oyster’s/clams soft body tissue movement Bivalves (oyster s, scallops, and clams) gastropods move by creeping along on their broad foot. ...may ooze a carpet of slippery mucus making it easier for them to move. mollusks that have two shells held together by hinges and strong muscles and are found in all kinds of watery environments obtaining food most are filter feeders strain tiny organisms from water using gills cilia on gills move food particles into the bivalve’s mouth movement larvae of most bivalves float or swim through the water Adults stay in one place or use their foot to move very slowly. Oysters attach to rocks movement protection Cephalopods (oc topuses, squi ds, nautiluses and cuttlefishes) larvae of most bivalves float or swim through the water Adults stay in one place or use their foot to move very slowly. Oysters attach to rocks clams move (a little) grain of sand gets between mantle and shell and irritates the soft mantle...the organism coats the irritant with nacre forming a pearl ocean dwelling mollusk whose foot is adapted to form tentacles around its mouth not all have shells (nautiluse have external shells, squid and cuttlefish have an internal small shell, octopus have no shells only mollusks that have closed circulatory system obtaining food cephalopods are carnivores captures prey using muscular tentacles then crushing prey in a beak and scrapes and cuts food with its radula tentacles contain sensitive suckers that can taste food without touching it by sensing chemicals in the water nervous system have large eyes and excellent vision most complex nervous system of any invertebrate....large brains and can remember things such as feeding times in captivity. movement swim by jet propulsion squeezing a current of water out of the mantle cavity through a tube. turning the tube they can change direction