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MOLLUSKS:

MOLLUSKS:. Slugs, snails, and animal that once lived in shells in the ocean or on the beach. Phylum Mollusca Range from slow-moving slug to jet-propelled squid Found in oceans, freshwater and moist terrestrial habitats.

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MOLLUSKS:

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  1. MOLLUSKS: • Slugs, snails, and animal that once lived in shells in the ocean or on the beach. • Phylum Mollusca • Range from slow-moving slug to jet-propelled squid • Found in oceans, freshwater and moist terrestrial habitats

  2. Oysters and mussels live firmly attached to the ocean floor or to the bases of docks or wooden boats. • Squid and the octopus swim freely • Slugs and snail crawl slowly over the forest floor.

  3. 100 000 species • Some have shells • Bilateral symmetry • True coelom • Two body openings • Muscular “foot” for movement • Mantle: thin membrane that surrounds the internal organs of the mollusk • In mollusks with shells, the mantle secretes the shell.

  4. How mollusks obtain food: • Radula: located within the mouth of a mollusk, is a tongue-like organ with rows of teeth. • The radula is used to drill, scrape, grate or cut food. • Some mollusks are grazers, some are predators, and some are filter feeders. • Bivalves do not have radulas, they are filter feeders.

  5. Reproduction in Mollusks: • Most have separate sexes and reproduce sexually. • Eggs and sperm are released at the same time into the water where external fertilization takes place. • Many gastropods are hermaphrodites. • Having the same individual produce both sperm and eggs increases the likelihood of fertilization in slow-moving animals.

  6. Nervous Control in Mollusks: • Simple nervous system with a brain and associated nerves that coordinate movement and behavior. • Paired eyes that range from simple cups that detect light to complex eyes in the octopus that have irises, pupils and retinas and function as well as the human eye.

  7. Circulation in Mollusks: • Well-developed circulatory system with a three-chambered heart. • Open circulatory: blood is pumped through vessels and into open spaces surrounding organs. • This exposes organs directly to blood containing oxygen and nutrients and easily removes wastes.

  8. Some mollusks (such as the octopus) has a closed circulatory system. • Closed circulatory system: blood moves through the body enclosed in a series of vessels

  9. Respiration in Mollusks: • Most mollusks have respiratory structures called gills. • Gills increase the surface area through which gases can diffuse. They are an extension of the mantle. • In land snails and slugs, the mantle has evolved into a primitive lung.

  10. Excretion in Mollusks: • Oldest known animals to have evolved excretory structures called nephridia • Nephridia: organs that remove metabolic wastes from an animal’s body. • Mollusks have one or two nephridia that collect wastes from the coelom. • Wastes are discharged into the mantle cavity, and expelled from the body by the pumping of the gills.

  11. Diversity of Mollusks: • Seven classes • These are the improtant 3 • Gastropoda • Bivalvia • Cephalopoda

  12. Gastropods: • One-shelled mollusks • Largest class • Stomach-footed (named for the way that the large foot is positioned under the body) • Slugs have not shell • Snails, abalones, conches, periwinkles, whelks, limpets, cowries and cones

  13. May be found in freshwater, saltwater, or moist terrestrial environments. • May be plant eaters, predators or parasites.

  14. Slugs: • No shell • Body is protected by a thick layer of mucus. • Nudibranchs: colorful sea slugs • Nudibranchs feed on jellyfish and incorporate their nematocysts into their own bodies which are expelled whenever a predator tries to feed on the slug.

  15. Bivalves: • Two-shelled mollusks • Clams, oysters and scallops • Most are marine, but a few a freshwater. • Range in size from 1 mm to 1.5 meters • No distinct head or radula • Most use their muscular foot for burrowing in the mud or sand at the bottom of the ocean or lake.

  16. A ligament like a hinge connects the two shells. • Filter feeders • Cilia beat to draw water into an incurrent siphon. • As water moves over the gills, food and sediment are trapped in mucus. Cilia that line the gills push the food particles into the stomach.

  17. The cilia also act as a sorting device. • Any rejected material is transported to the mantle where it is expelled through the excurrent siphon.

  18. Cephalopods: • Head-footed mollusks • All marine • Octopus, squid, cuttlefish, and chambered nautilus

  19. The only cephalopod with a shell is the chambered nautilus. • The cuttlefish has a reduced internal shell. • Very complex structures • Predators that swim or walk over the ocean floor pursuing their prey. • They grab prey with their tentacles.

  20. The foot has evolved into structures with hooks, suckers or adhesive structures. • The tentacles bring the prey to the mouth where it is bitten by the beak-like jaw. • The food is then pulled into the mouth by the radula.

  21. Possess siphons that expel water. • By expelling water forcefully, these mollusks can move quickly by jet propulsion. • Squids can attain speeds of 20 meters per second with this method. • They also expel “ink” to confuse and escape predators.

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