Mollusca II: Scaphopods & Cephalopods

• Scaphopods

  Tusk Shells
• Scaphopods


  • Burrow in sediments with the mouth downwards
  • Mostly subtidal (and deep) (below level of tide)
  • No ctenidia (gills) or osphradium
  • Gas exchange via mantle
  • Sensing through posterior mantle
  • They have a linear, L-shaped through gut, 1 pair nephridium
  • Gonad empties into the right nephridium
  • Eggs released into excretory system and through excretory system
  • Have muscular foot to help dig and burrow into sediment, and also works like a plunger; also expel the water our posterior end of shell
  • Captacula - (100-200) search for and capture food, convey to mouth
• Cephalopod origins


  1. Nautilus still alive, oldest lineage

  2. Ammonoid and belemnite extinct

  3. First lineage of cephalopods had external shells

  4. Chambered

  5. Divided by septa

  6. Connected by siphuncle (S)

  7. BC stands for body chamber, organism only occupies body chamber and grows out into outer

  8. Siphuncle fills those chambers with gas, gas is buoyant so as animal gets heavier as it gets older, it helps it stay buoyant (neutrally)

  9. Among living organism, only nautiloids still have a shell amongst cephalopods

  10. More derived groups have related structure

  11. The nautilus shell is a near perfect logarithmic spiral
• Gladius


  The pen of modern squids
• Adaptations in Cephalopods


  • Locomotion in nautiloids is by propulsion of water through a siphon (funnel)
  • Draw in water through mantle, push out through siphon (creates jet propulsion)
  • Hard external shell limits the amount of increase in body volume
  • Uncoiling, internalization, softening of shell ⇒ increased propulsion ability
  • Octopodiformes ⇒ in the form of octopods
• Circulatory Systemof Cephalopods


  • Among mollusks, only cephalopods have entirely closed circulatory system
  • Separate hearts for body (systemic) and gills (branchial)
• Visual, Defense, Communications

  • Have three kinds of cells controlling skin colorization: chromatophores, iridophores, photophores
  • Also have ink sac to release a cloud of smoke to avoid/hide/confuse
  • Nautiloids lack all but the ink cell
• Cephalization


  • Extremely complex nervous system!
  • 80 M neurons in central nervous system
  • 300 M neurons in peripheral nervous system
  • Chemo, tactile and light sensors in arms
  • Evidence of REM eye twitching in sleep!
  • Well developed brian with many lobes!
  • True "camera style" image forming eyes (better than vertebrates eyes)
  • Capable of learning (visual, memory communication)

  
• Function of captacula?


  Search for food and convey to mouth