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Phylum Molluska

Phylum Molluska. Characteristics of Mollusks. Aquatic (freshwater, marine) & Terrestrial External or internal shell or no shell Size: small (i.e. grain of sand) to large (20 meter squid) Bilateral Symmetry . Circulatory System of Mollusks.

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Phylum Molluska

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  1. Phylum Molluska

  2. Characteristics of Mollusks • Aquatic (freshwater, marine) & Terrestrial • External or internal shell or no shell • Size: small (i.e. grain of sand) to large (20 meter squid) • Bilateral Symmetry

  3. Circulatory System of Mollusks • Open in most, blood not confined to vessels (example: snails, slugs) • Closed in others, blood is confined to vessels(example: squid, octopi)

  4. Larvae = trochophore • Free swimming • Young form of animal • Looks and behavesdifferently fromadult

  5. Body Plan of ALL Mollusks • FOOT - used for movement; contains mouth • VISCERAL MASS - internal organs • SHELL – made of calcium carbonate; not all mollusks have • MANTLE – a thin membrane that surrounds and secretes the shell

  6. Reproduction – mainly external fertilization • Most are separate sexes • Release sperm and eggs into the water • Some are hermaphrodites • Some water snails and some oysters • Land mollusks have internal fertilizations • Male has a penis to transfer sperm

  7. Class Bivalvia “Bivalves”

  8. Bivalvia(Clam, oyster, scallop, mussel) • Have 2 VALVES (shells) held together by a ligament held together • Shell stays shut by adductor muscles • They are FILTER FEEDERS • Food and water enter the incurrent siphon; food taken in by mouth • Can accumulate toxins from the surrounding environment • GILLS for respiration

  9. Mussels attach to rocks with their BYSSUS THREADS (sessile)

  10. Scallops FLAP their shells to swim • http://www.youtube.com/watch?v=_2iXHBuSIJY

  11. Clams burrow into sand/mud with their FOOT • http://www.youtube.com/watch?v=HrBijKf0Ywk

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