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Daily Opener

Daily Opener. Mollusks are soft bodied animals that can have either an internal or external shell. Based on this definition, name 3 animals that you think belong to the Phylum Mollusca . Daily Opener. Why are mollusks grouped in the same phylum?. Phylum Mollusca. Chapter 27.4

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Daily Opener

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  1. Daily Opener • Mollusks are soft bodied animals that can have either an internal or external shell. • Based on this definition, name 3 animals that you think belong to the Phylum Mollusca.

  2. Daily Opener • Why are mollusks grouped in the same phylum?

  3. Phylum Mollusca Chapter 27.4 Essential Question: What are the defining characteristics of Mollusks?

  4. What is a Mollusk? • Soft-bodied animals that have an internal and external shell. • There are over 150,000 speciesof mollusks. • Includes snails, slugs, clams, squids, and octopi. • Grouped in the same phylum because they have similar developmental stages. • Free-swimming larval stage: trocophore.

  5. Body Plan • Different body shapes are variations on a single body plan with 4 basic parts: • Foot-movement • Mantle-thin layer of tissue that covers body • Shell-hard covering made by glands that secrete calcium carbonate • Visceral Mass-contains internal organs

  6. Feeding • Mollusks can be herbivores, carnivores, detrivores, filter feeders, or parasites. • Some mollusks feed using a radula (tongue-shaped structure). • Others have siphons which allow water to flow through the body trapping food particles.

  7. Respiration • Aquatic mollusks such as clams, snails, and octopi breathe using gills inside their mantle cavity. • Land snails and slugs respire using a mantle cavity that has a large surface area lined with blood vessels. • The oxygen diffuses across the surface.

  8. Circulation • Circulatory systems carry oxygen and nutrients to all parts of the mollusk body. • Open-blood is pumped through vessels by a simple heart. • Blood eventually leaves the vessels and works its way through different sinuses (large saclike space). • Found in clams. • Closed-transports blood much more quickly. • Found in octopi and squid.

  9. Excretion • Cells release ammonia into the blood. • Tube-shaped nephridiaremove this ammonia from the blood and release it to the outside.

  10. Response • The complexity of the nervous system differs among mollusks. • Clams have a simple nervous system with eyespots, few nerve cords, and chemical receptors. • More complex mollusks such as octopi have well-developed brains.

  11. Movement • Mollusks move in different ways. • Snails secrete mucus to move over surfaces. • Octopi use jet propulsion to draw water into their cavity and force it out through their siphon. • This propels the organism in the opposite direction.

  12. Reproduction • Some snails and 2-shelled mollusks reproduce sexually by external fertilization. • They release large numbers of eggs and sperm into open water. • The eggs are fertilized in the open water and develop into larva. • Other snails and tentacled mollusks reproduce by internal fertilization. • This takes place inside the body of the female. • A few mollusks are hermaphroditic.

  13. Gastropods, Bivalves, Cephalopods Major classes of Mollusks

  14. Class Gastropoda • Gastropods: snails, slugs, conch • Largest class (70, 000 named species) • Shell-less or single-shelled mollusks • Move by using muscular foot located on ventral side. • When threatened shelled gastropods can pull completely into themselves. • Gastropods that have no shell will often secrete chemicals that are poisonous.

  15. Class Gastropoda • Feeding Habits • Most are herbivores-scrape algae off surfaces with radula • Carnivores-have radula modified into drill to bore through shells of other mollusks • Scavengers-eat dead organisms

  16. Class Bivalvia • Bivalves - 2 shells held together by powerful muscles • Include clams, oysters, mussels, scallops • No head or radula • Filter feeders – food particles get trapped in mucus lining the gills • Not much movement • Sessile • Clams dig into mud • Scallops flap shell in short bursts

  17. Bivalves - Scallop

  18. Anatomy

  19. Class Cephalopoda • Cephalopods – squid, octopi, cuttlefish, nautilus • Soft bodied with a head attached to a single foot that is divided into arms. • Most have an ink sac that secretes sepia, a dark colored fluid containing melatonin. • When a predator attacks, the animal ejects the ink into the water where it hangs between the animal and the predator allowing for a quick escape.

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