Lecture 15

Question 1

Amount

Answer 1

About 750 - 900 total extant cephalopod species

Question 2

Protective anatomy - nautiloidea

Answer 2

• Basal member of Cephalopoda
• Exterior chambered shell
  
  • Highly sought after nay poachers/commercial entities
• Soft body always occupies the ‘newest’ chamber
  
  • Chambers are sealed and filled with cameral fluid during growth

Question 3

Molluscan heritage

Answer 3

• Relaxation phase
  
  • Mantle muscles relax to expand the mantle cavity
  • Water enters behind hood
  • Siphon and buccal mass close to prohibit water exit
• Contraction phase
  
  • Circular muscles around mantle contract, building pressure within mantle cavity
• Jet propulsion
  
  • Siphon bursts open, flexible funnel controls direction
  • Opposing direction

Question 4

Built in buoyancy

Answer 4

• Maintained by manipulating cameral fluid density and nitrogen gas content of chambers
• Siphuncle is a tube of tissue surrounded by a calcareous casing that runs along all chambers
  
  • Septa act as braces for the chambers
  • Junctions between septa are sutures

Question 5

The descent

Answer 5

• Nautilus begins to descend
  
  • Fluid moves up siphuncle into chambers due to ambient pressure
  • Increases density of the shell, reducing buoyancy
• Nautilus reaches desired depth
  
  • Siphuncle actively transports ions from chambered cameral fluid into hemolymph, water must exit the chamber by osmosis
  • Lost water volume is replaced within nitrogen gas, increasing buoyancy

Question 6

The reward

Answer 6

• Nautilus are olfactory and tactile predators
  
  • Enlarged olfactory lobes
  • Pin-hole eyes; poor vision
  • Modified appendages (x10) with many cirri (about 100 total)
• Primarily feeds on tiny benthic prey and detritus
  
  • Curiously does not attack live shrimp, even when on feeding apparatus

Question 7

The ascent

Answer 7

• Nautilus ascends towards surface
  
  • Chambered gas expands, passively increasing buoyancy… nautilus cannot actively refill these chambers, must wait

Question 8

Cephalopoda dominance

Answer 8

• Nautilus amongst the first buoyant swimming predators
  ADVANTAGES:
• To be armoured although slow moving muscular ‘submarine’ with tentacles and keen olfactory perception
  DISADVANTAGES:
• Long maturation (about 20 years) to lay dozens of eggs

Question 9

The push for convergence-post-devonian era

Answer 9

• Faster and more energetically efficient predators than shelled Cephalopoda
• Protective shell likely became less evolutionary favourable due to speed
• Shelled cephalopods largely succeed in deeper water where fish were less adaptive

Question 10

Ocean acidification

Answer 10

• Some Mollusca shells dissolve in CO2- enriched acidified seawater