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Chapter 6, Section 3 Soft-bodied invertebrates that usually have a shell (ex. Snails, mussles, octopus) Have mantle and large muscular foot Mantle: thin layer of tissue that covers the mollusk’s soft body Water-dwelling Gills: organs in which carbon dioxide from the animal is exchanged for oxygen in the water Land-dwelling mollusks have gills mollusks have lungs Lungs: carbon dioxide from the animal is exchanged for oxygen in the air Have digestive systems with two openings Have scratchy, tonguelike organ called radula Radula: has rows of fine, teethlike projections used to scrape off small bits of food Have open circulatory system Do not have vessels to contain blood Blood washes over organs Gastropods Largest group of mollusks Have one shell Live in water or on land Move about on a large, muscular foot Secretion of mucus allows them to glide Bivalves Has two shells joined by a hinge Large, powerful muscles open & close shell Gills filter water for food Cephalopods Most complex type Have internal plate instead of shell Closed circulatory system Adapted for quick movement in ocean Have mantle surrounding internal organs Annelids (earthworms, leeches, marine worms)- body made of repeating segments or rings that make worm flexible Each segment has nerve cells, blood vessels, part of digestive system, coelom Internal body cavity, separates internal organs from body wall Closed circulatory system Complete digestive system with two body openings What are the characteristics of annelids?