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Phylum Mollusca. Characteristics. Soft body Usually have an internal or external shell Bilateral symmetry Word mollusca means “soft” More complex organ system Coelomates Muscular No skeleton. Body Plan. Many different shapes Most have 4 main parts Foot: usually for movement
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Characteristics • Soft body • Usually have an internal or external shell • Bilateral symmetry • Word mollusca means “soft” • More complex organ system • Coelomates • Muscular • No skeleton
Body Plan • Many different shapes • Most have 4 main parts • Foot: usually for movement • Mantle: thin layer of tissue that covers body • Shell: calcium carbonate • Visceral mass: beneath the mantle; consists of internal organs
Feeding • Radula – rough tongue or ribbon of teeth • Herbivores, scavengers, carnivores, omnivores
Respiration • Aquatic- Breath using gills inside their mantle cavity • Land-mantle cavity lined with blood vessels • Must be kept moist for diffusion
Circulation • Either closed or open circulatory system • Open-simple heart • Octopi and squid-closed (no heart like earthworm) • Snails and slugs- open
Excretion • All mollusks have a full excretory system. • Cells called nephridia remove ammonia from blood and release it outside the body. • One way digestive system – mouth to anus • Squid have a tube-like structure called a siphon through which water enters and leaves
Response • Snails, clams, etc have a simple nervous system • Few ganglia and nerve cords near mouth • Simple sense organs • Chemical receptors • Eye spots
Response • Cephalopods like Octopi have a complex nervous system • Most complex of the invertebrates • Well developed brain • Can be trained!
Reproduction • All mollusks reproduce sexually • Some are dioecious • External fertilization • Some are monoecious
Habitat • Terrestrial • Marine • Freshwater • Rocky shores
Classes • Class Gastropoda – snails, slugs • Class Cephalopoda – octopus, squid, nautilus • Class Bivalvia – oysters, clams
Gastropods • Largest group of mollusks • “stomach foot” • 0 to 1 shell • Movement on foot – slippery mucus • radula
Bivalves • 2 shells held by hinge • No radula – filter feeders • Mostly sessile • Grain of sand that gets stuck between mantle and shell causes bivalve to produce mucus – pearl • Found in all water environments • Omnivores
Cephalopods • “Head foot” • Ocean dwelling • Foot forms tentacles around mouth (8 or more) • Carnivores with radula • Swim by jet propulsion • Nautilus-external shell • Squids-small internal shell • Called a Penn • Octopus- no shell