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Clams, Oysters, etc. Team Awesome. General Characteristics. Most are marine, some freshwater, some land (some snails and slugs) Basic characteristics of Mollusks (Mollusca) Soft body, covered by dorsal shell (CaCo3) Broad, flat, muscular foot used for locomotion

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general characteristics
General Characteristics
  • Most are marine, some freshwater, some land (some snails and slugs)
  • Basic characteristics of Mollusks (Mollusca)
    • Soft body, covered by dorsal shell (CaCo3)
    • Broad, flat, muscular foot used for locomotion
    • Body organs(visceral mass) above the foot
    • A mantle- thin sheet of tissue thatcontains gills and other structures. It covers the visceral mass and usually contains glands that secrete a shell.
    • Rasplike structure called a radula which is a belt of teeth in the mouth region (not clams)
    • The main body cavity is typically a hemocoel.
classes of phylum
Classes of Phylum
  • Polyplacophora- chitons-primitive marine animals with shells, 8 transverse plates, head reduced broad foot used for locomotion
  • Gastropoda- Snails, slugs, nudibranchs- marine, freshwater and terrestrial; coiled shell in many species; torsion of visceral mass; well developed head with tentacles and eys
  • Bivalvia- clams, oysters, mussels- Marine or freshwater; body laterally compressed; two part shell hinged dorsally; hatchet shaped foot; suspension feeders.
  • Cephalopoda- squids, octopods- marine; predatory; foot modified into tentacles, usually bearing suckers; well developed eyes; closed circulatory system.
class bivalvia
Class Bivalvia
  • clams, oysters, mussels
  • Marine or freshwater
  • Body laterally compressed
  • Two part shell hinged dorsally
  • hatchet shaped foot
  • suspension feeders.   
  • Two-part shell(valves) hinges dorsally opens ventrally
  • Inner shell (CaCo3)
  • Connected by elastic ligament
    • adductor muscles allow it to close
  • Nervous system composed of three pairs of ganglia, tow pairs of nerve cords, and variety of sense organs.
    • pigmented eye spots(ocelli) present at edge or mantle    
feeding practices
Feeding Practices
  • Suspension Feeders
    • Trap food particles in sea water
    • Take water in through extension of mantle (incurrent siphon)
    • Water leaves through excurrent siphon.
    • As water passes over gills, food particles trapped in mucus secreted by gills
    • Cilia move food to mouth.
    • Oyster can filer more than 30L/hr
    • No radula
response to stimuli
Response to Stimuli
  • Clams have low response to stimuli when siphon opening is widely distended
  •  Ocelli enables animals to detect changes in light intensity
  • Two distinct sexes sperm are shed in water and fertilize the eggs within the female.
  • Female carries her young within mantle cavity
  • Development takes place in gill filaments of female.
  • Marine bivalve->trochophore larva->veliger larva.
  • Some freshwater bivalves->glochidium (modified larval stage), parasites on gills of fishes.