`Mollusks Phylum Mollusca Soft-bodied invertebrate covered with protective mantle that may or may not form a hard, calcium carbonate shell Includes chitons, snails, slugs, clams, oysters, squid, octopus, & nautilus Second largest animal phylum Have a muscular foot for movement which is modified into tentacles for squid & octopus Complete, one-way digestive tract with a mouth & anus Have a fully-lined coelom (eucoelomate) Cephalization - have a distinct head with sense organs & brain Have a scraping, mouth-like structure called the radula Go through free-swimming larval stage called trochophore Trochophore Larva Body organs called visceral mass lie below mantle Have circulatory, respiratory, digestive, excretory, nervous, & reproductive systems Bilaterally symmetrical
Most have separate sexes that cross-fertilize eggs Gills between the mantle & visceral mass are used for gas exchange Includes 4 classes --- Polyplacophora (chitons), Gastropoda (snails, slugs, nudibranchs, conchs & abalone), Pelecypoda or Bivalvia (clams, oysters, & mussels), & Cephalopoda (squid, octopus, & nautilus) Class Polyplacophora SNAIL, CLAM, CHITON, & SQUID All marine Have a shell divided into 8 over-lapping plates Live on rocks along seashore feeding on algae CHITON
Class Gastropoda Head has a pair of retractable tentacles with eyes located at the ends Have a single shell or valve (snails) or none (slugs) Known as univalves Snails * May be marine, freshwater, or terrestrial * Aquatic snails breathe through gills & use their radula to scrape algae for food * Terrestrial snails use their mantle cavity as a modified lung & saw off leaves * Have open circulatory system * Land snails are hermaphrodites * Aquatic snails have separate sexes * Use internal fertilization
SLUG Pteropods * Called "sea butterflies" * Marine * Have a wing-like flap for swimming "SEA BUTTERFLY" Oyster Drills * Radula modified to drill into oyster shells OYSTER DRILL
Nudibranch * Marine slug * Lacks shell NUDIBRANCH Class Bivalvia or Pelecypoda Sessile or sedentary Includes marine clams, oysters, shipworms, & scallops and freshwater mussels Filter feeders Have two-part, hinged shell (2 valves) Have muscular foot that extends from shell for movement Scallops clap valves together to move
Shell secreted by mantle & made of 3 layers --- outer horny layer protects against acids, middle prismatic layer made of calcium carbonate for strength, & inner pearly layer next to soft body Mantle secretes substance called "mother of pearl" to surround irritants like grains of sand Oldest, raised part of shell called umbo Powerful anterior & posterior adductor muscles open & close shell Lack a distinct head Have an incurrent & excurrent siphon that circulate water over the gills to remove food & oxygen INTERNAL CLAM ANATOMY Have heart & open circulatory system
Nervous system made of 3 pairs of ganglia, nerve cords, & sensory cells that detect light, chemicals, & touch Separate sexes with external fertilization of eggs Class Cephalopoda or Amphineura Includes octopus, squid, cuttlefish, & chambered nautilus All marine NAUTILUS OCTOPUS Most intelligent mollusk Well developed head Active, free swimming predators Foot divided into tentacles with suckers Use their radula & beak to feed Closed circulatory system SQUID
Lack an external shell Highly developed nervous system with vertebrate-like eyes Separate sexes with internal fertilization Squid * Largest invertebrate is the Giant Squid * Large, complex brain * Ten tentacles with longest pair to catch prey * Use jet propulsion to move by forcing water out their excurrent siphon * Chromatophores in the skin can help change squid color for camouflage * Can squirt an inky substance into water to temporarily blind predators * Have internal shell called pen * Female lays eggs in jellylike material & protects them until hatching Octopus GIANT SQUID * Eight tentacles * Similar to squid * Crawls along bottom looking for prey OCTOPUS
Chambered Nautilus * Has an exterior shell * Lives in the outer chamber of the shell * Secretes gas into the other chambers to adjust buoyancy NAUTILUS Economic Importance of Mollusks Used by humans for food Pearls from oysters Shells used for jewelry Do crop & garden damage Serve as intermediate hosts for some parasites such as flukes