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MOLLUSKS:

MOLLUSKS:. Section 27 – 1 Slugs, snails, and animal that once lived in shells in the ocean or on the beach. Phylum Mollusca. 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. 100 000 species

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MOLLUSKS:

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  1. MOLLUSKS: • Section 27 – 1 • Slugs, snails, and animal that once lived in shells in the ocean or on the beach. • Phylum Mollusca

  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

  3. 100 000 species • Some have shells • Bilateral symmetry • True coelom • Two body openings • Muscular “foot” for movement

  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.

  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.

  6. Larval stages: • Larval stages of all mollusks are similar.

  7. Nervous Control in Mollusks: • Simple nervous system with a brain and associated nerves that coordinate movement and behavior.

  8. 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.

  9. Some mollusks (such as the octopus) has a closed circulatory system.

  10. 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.

  11. Excretion in Mollusks: • Oldest known animals to have evolved excretory structures called nephridia • Nephridia: organs that remove metabolic wastes from an animal’s body.

  12. Diversity of Mollusks: • Seven classes • Gastropoda • Bivalvia

  13. Gastropods: • One-shelled mollusks • Largest class • Stomach-footed (named for the way that the large foot is positioned under the body)

  14. May be found in freshwater, saltwater, or moist terrestrial environments.

  15. Slugs: • No shell • Body is protected by a thick layer of mucus. • Nudibranchs: colorful sea slugs

  16. Bivalves: • Two-shelled mollusks • Clams, oysters and scallops • Figure 27-7 • Most are marine, but a few a freshwater. • Range in size from 1 mm to 1.5 meters

  17. A ligament like a hinge connects the two shells. • Filter feeders • Cilia beat to draw water into an incurrent siphon.

  18. The cilia also act as a sorting device.

  19. Cephalopods: • Head-footed mollusks • All marine

  20. The only cephalopod with a shell is the chambered nautilus. • The cuttlefish has a reduced internal shell. • Very complex structures • .

  21. 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. • Figure 27-8

  22. 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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