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Chapter 9 The Mollusks

Chapter 9 The Mollusks. Abalone. Mollusks. Soft bodied Include the shipworm, snail, clam, mussel, oyster, scallop, abalone, squid, octopus, cuttlefish, chambered nautilus May or not have a shell 100,000 species. More Mollusk Characteristics. Soft, bilaterally symmetrical bodies

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Chapter 9 The Mollusks

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  1. Chapter 9The Mollusks Abalone

  2. Mollusks • Soft bodied • Include the shipworm, snail, clam, mussel, oyster, scallop, abalone, squid, octopus, cuttlefish, chambered nautilus • May or not have a shell • 100,000 species

  3. More Mollusk Characteristics • Soft, bilaterally symmetrical bodies • Head, foot, coiled visceral mass (internal organs) • Coelom (body cavity), brain (like the worms)

  4. 9.1 Class Bivalvia • Clams, oysters, scallops, mussels • 2 shells held together by adductor muscles • Clams are the most common and are fed on by sea stars and predatory snails • You can learn the age of a clam by counting the bands on its shell • Little lines make up the bands and 1 band = 1 year

  5. Clam Age

  6. Clam Shells • Wider age bands mean a better year with more favorable conditions. • Made of CaCO3 which is secreted by the mantle

  7. Life Activities • Siphons – Incurrent siphon takes in water and food and waste is excreted through the excurrent siphon. • Clams filter food out of the water and O2 diffuses into gill membranes and CO2 diffuses out into waste water. • Clams filter and clean great quantities of seawater

  8. More Life Activities • Open circulatory system with colorless blood • One way digestive tract • Mussels excrete byssal threads to keep them anchored to rocks – very strong • Oysters excrete cement

  9. Movement • Clams dig into sand using muscular foot and extend their incurrent siphon into the water above them • Scallops clap shells together and move by jet propulsion

  10. Reproduction • Separate sexes • Females excrete eggs into the water and males excrete sperm. • Fertilization is external and larva lives as part of zooplankton population until it forms a tiny shell and settles to bottom

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