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Phylum Mollusca

Explore the diverse characteristics of mollusks, including coelomates, mantle structure, and trochophore larva, along with a focus on Gastropoda, Bivalvia, and Cephalopoda classes. Discover the unique anatomy and behaviors of clams, octopus, and snails.

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Phylum Mollusca

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  1. Phylum Mollusca Soft – bodied invertebrates Clams, Octopus, Snails

  2. Characteristics • Coelomates • Trochophore larva (aquatic molluscs) • Divided into head – foot and visceral mass • Visceral mass contains the hear and organs for digestion, excretion, and reproduction • Coleom surrounds the heart

  3. Mantle, epidermal tissue secretes the shell • Calcium carbonate • Gills • Found within the mantle cavity • Most are bilaterally symmetrical • Nervous system • Pair of ganglia in head – foot and visceral mass • Radula

  4. Phylum Mollusca Divided into 7 classes • Focusing on 3 classes • Gastropoda, one or no shell (snails) • Bivalvia, two shells with hinge (clams) • Cephalopoda, tentacles (octopus)

  5. Snapshot of Mollusca Diversity

  6. Class Gastropoda • Largest and most diverse group • Single shell • Torsion • Larval development visceral mass twists 180 degrees in relation to the head • Brings anus, gills, and mantle cavity in the front • Allows adult to pull itself into the cavity when threatened

  7. Moves by using wave – like motion of foot • Open circulatory system • Hemolymph • Flows into hemocoel (blood cavity) • Separate Sexes but may be hermaphroditic

  8. Class Bivalvia • Shell is divided into 2 halves (valves) and connected by a hinge • Close the shell by contracting is adductor muscles, open by relaxing them • Three layers secreted by mantle • 2nd layer consists of calcium carbonate

  9. Bivalvia • Sessile (foot) • Filter – feeders • Nervous system • 3 pr of ganglia (mouth, digestive system, foot)

  10. Clams • Bury in mud • Siphons extend past shell • Cillia on the gills pull water in the incurrent sipon • Water/food particles pass over the mucus on the gills and food becomes trapped • Oxygen is absorbed • Water exits the clam through the excurrent siphon

  11. Clam Anatomy

  12. Separate sexes • Gametes are released into water • Trochophore larvae • Freshwater clams

  13. Class Cephalopoda • Head – foot • Specialized for free – swimming predatory life • Circle of tentacles from the head • Beak • Advanced nervous system • Lobes with nerve cells • Sensory system

  14. Closed circulatory system • Rapid movement of materials • Separate sexes • Egg into juvenile without trochophore larva • Chromatophores

  15. Squid/Cuttlefish • 10 tentacles • Internal shell

  16. Octopuses • 8 tentacles

  17. Chambered Nautiluses • Retains external shell • Coiled and divided into series of gas – filled chambers • Soft – body moves forward as the organism grows • Buoyant

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