Molluska

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Chapter 35

• Section 1
• Molluska

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Characteristics of Mollusks

• Some are filter-feeders while others are
  fast-moving predators with complex nervous
  systems
• Coelomates- true body cavity

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Characteristics of Mollusks

• Aquatic mollusks have a larval stage of
  development called a trochophore
• Trochophores are motile and disperse throughout
  bodies of water

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Body Plan of Mollusks

• 2 main regions- head-foot visceral mass
• Head-foot- consists of the head, mouth, sensory
  structures, and foot- large muscular organ
  usually used for locomotion

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Body Plan of Mollusks

• Visceral mass- (located above the head-foot)
  contains the heart, organs of digestion,
  excretion, reproduction
• Visceral mass is covered by a layer of epidermis
  called the mantle

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Body Plan of Mollusks

• Most mollusks- mantle secretes hard shells
  containing calcium carbonate
• Why have a shell???

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Body Plan of Mollusks

• Mantle cavity- space between the mantle and
  visceral mass
• Gills are protected by mantle cavity

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Body Plan of Mollusks

• Ganglia- more complex nervous system that
  controls locomotion, feeding, and sensory
  information (light, touch, etc)

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Body Plan of Mollusks

• Radula- main feeding adaptation
• Tongue-like strip of tissue covered with tough,
  abrasive teeth that point backwards
• Terrestrial snails- cut through leaves
• Aquatic snails- scrape algae

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Class Gastropoda

• Gastropods
• snails, conchs
• slugs nudibranchs

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Snail
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Conch
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Slug
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Nudibranch
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Class Bivalvia

• Bivalves- two shells connected by a hinge
• Closes its shell with adductor muscles, when the
  muscles relax, the valves open
• Most bivalves are sessile

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Class Bivalvia

• Clams
• Bury in sand or mud
• Feeding Cilia beats on the gills and set up a
  current of water that enters through the
  incurrent siphon and leaves though the excurrent
  siphon

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Clam
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Class Cephalopoda

• Cephalopod- head foot
• Free-swimming have tentacles
• Nervous system is advanced- cephalopod brain is
  largest invertebrate brain
• Ex Octopi can perform tasks distinguish
  between objects

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Class Cephalopoda

• Release dark fluid to distract predators
• Chromatophores- pigment cells that allow the
  organism to change colors quickly

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Squid

• Move by pumping in water though their siphons
• Largest invertebrate- Architeuthis- 60 feet long
  and up to 2,000 lbs!

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Octopus
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REVIEW!!!

• What purpose does a radula have?
• Describe the characteristics of mollusks.
• Name the three major classes of mollusks an
  example of each.