Class Cephalopoda
The Quest for Speed

Defense strategies (if you’re sessile or slow)

• Stinging organelles
• Cnidarians
• Armor (internal and external)
• Widespread
  • E.g., Cambrian, corals, arthropods, etc.
• Often secondarily lost (opisthobranchs, cephalopods, we’ll see in some echinoderms & the vertebrates)
• Noxious secretions
• E.g., sponges, nudibranchs
• Speed

Requirements of speed

• Improve
• Respiratory systems
• Digestive system
• Prey capture
• Locomotion
• Circulation
• Sensory systems
• Nervous system
• etc.

Cephalopod synapomorphies

• Foot modified to form
• Tentacles
• Siphon
• Closed circulation

Cephalopod synapomorphies

• Foot modified
• Closed

• Beak

Cephalopod synapomorphies

• Foot modified
• Closed circulation
• Beak
• Brain in braincase

Cephalopod synapomorphies

• Foot modified
• Closed circulation
• Beak
• Brain in braincase
• Ink sac

Cephalopod synapomorphies

• Foot modified
• Closed circulation
• Beak
• Brain in braincase
• Ink sac
• Septate shell
• Siphuncle

Cephalopod synapomorphies

• Foot modified
• Closed circulation
• Beak
• Brain in braincase
• Ink sac
• Septate shell
• Siphuncle

Septa and Siphuncle

• Used for buoyancy control
• Chamber filled with gas and/or fluid
• Fluids withdrawn using siphuncle
• Osmosis
• Slow!
• Need to swim up and down
• Chambers not pressurized!
• Risk of implosion at depth

Class Cephalopoda - three subclasses

Subclass Nautiloidea

• A "living fossil" of sorts
• Formerly abundant, diverse
• Only six species remain
• Restricted to deep water in the South Pacific
• Only living cephalopod with an external shell
• Coiled in modern
• Coiled or straight in fossils

Subclass Nautiloidea

• Up to 90 tentacles
• Suckerless, but adhesive
• 4 in males for reproduction
• Daily vertical migration
• Feeds on a variety of prey
• Crustaceans
• Scavenging

Subclass Ammonoidea

• Formerly very diverse
• Repeated radiation and extinctions
• Entire group went extinct at the end of the Cretaceous

Subclass Ammonoidea

Subclass Ammonoidea

• Similar to Nautiloids in having external, chambered shell, but …

Subclass Ammonoidea

• Similar to Nautiloids in having external, chambered shell, but …
• Siphuncle ventral
• Septa usually very complex
• Increase resistance to predation, implosion
• Increase surface area for exchange of gases in chamber

Cephalopod Shell Evolution

• Primitively from monoplacophoran type shell
• Developed septa
• Visceral support (?)
• Or may have developed concurrently with elongation of shell

Cephalopod Shell Evolution

• Elongation of shell…
• heavy!
• Gas filled chambers
• Bouyancy
• Stability

Cephalopod Shell Evolution

• Horizontal orientation
• Allows streamlining
• High speed locomotion
• Problems
• Unwieldy - up to 5 m
• Center of mass forward of center of buoyancy
• Requires ballast

Cephalopod Shell Evolution

• Coiling
• Brings center of buoyancy over center of mass
• More maneuverable
• Present in
• Nautiloids
• Ammonoids

Subclass Coleoidea

• Shell internal or absent
• Reduces weight
• Eliminates need for coiling or ballast
• Allows high speed!
• Suckers or hooks
• Better prey capture
• Reduction to one pair of vascularized ctenidia
• Reduces mantle crowding

Subclass Coleoidea - Four orders

• Sepioidea
• Cuttlefish
• Decapoda
• Squids
• Octopoda
• Octopuses
• Vampyromorpha
• Vampire squids

Order Sepioida

• Short, broad body
• Eight arms + 2 tentacles
• Lateral fins
• Suckers only (on tips)

Order Sepioida

• Short, broad body
• Eight arms + 2 tentacles
• Lateral fins
• Suckers only (on tips)
• Shell internal
• Cuttlebone

Order Decapoda

• Elongate
• Lateral fins
• Shell very reduced
• pen

Order Decapoda

• Elongate
• Lateral fins
• Shell very reduced
• Eight arms + 2 tentacles
• Often have hooks

Order Decapoda

• Elongate
• Lateral fins
• Shell very reduced
• Eight arms + 2 tentacles
• Largest invertebrate
• Architeuthis - 20 m

Order Decapoda

Order Decapoda

• Elongate
• Lateral fins
• Shell very reduced
• Eight arms + 2 tentacles
• Largest invertebrate
• Very fast, active predators
• Can be ecologically dominant

Order Octopoda

• Rounded
• Lateral fins usually absent
• Shell absent or vestigial
• Eight arms
• Usually benthic
• Secondary crawling habit

Order Vampyromorpha

• One species
• "Plump", fleshy
• O2 minimum layer
• Lateral fins present
• Shell vestigial
• Eight arms + two filaments
• Bioluminescent

Cephalopod Locomotion

• Reduction of shell, as in Coleoidea, advantageous
• Saves the energy of producing a shell
• Reduces weight
• Allows faster locomotion
• No risk of implosion
• But ...
• Harder to be neutrally buoyant
• No protection from predators by shell

Cephalopod Locomotion

• Five general types:
• Jet propulsion
  • Found in all cephalopods
  • Water propelled out siphon
  • Radial muscles expand cavity
  • Circular muscles contract
  • Pallial, siphonal valves

Cephalopod Locomotion

• Five general types:
• Jet propulsion
• Lateral fin undulation
  • Common in squid, cuttlefish
  • Slow, but efficient
  • Maneuverable

Cephalopod Locomotion

• Five general types:
• Jet propulsion
• Lateral fin undulation
• Lateral fin flapping
  • Squid, some octopus
  • Moderately fast, very efficient

Cephalopod Locomotion

• Five general types:
• Jet propulsion
• Lateral fin undulation
• Lateral fin flapping
• Umbrellar locomotion
  • Common in Octopoda

Cephalopod Locomotion

• Five general types:
• Jet propulsion
• Lateral fin undulation
• Lateral fin flapping
• Umbrellar locomotion
• Crawling
  • Primarily Octopoda

Cephalopod Feeding

• Well developed beak
• Allows predation on hard prey
• Biting of chunks out of larger prey
• Reduction of prey to more digestable pieces
• Some species (the blue ringed octopus) have poison gland (modified salivary gland)

Cephalopod Circulation/Respiration

• Circulation:
• Closed
• Three hearts
  • One systemic to body
  • Two branchial to gills
• Relatively high pressure
• Countercurrent exchange of gases

Cephalopod Circulation/Respiration

• Countercurrent exchange

Cephalopod Nervous system

• Large brain
• Information processing
• Giant axons
• Speed proportional to size
• Stellate ganglia ensure coordinated, forceful contraction -> speed!

Cephalopod Sensory system

• Well developed eyes
• Nautiloids
• Simple pinhole camera eyes
• Coleoids
• Complex, image forming eyes Iris, lens, cornea
• Convergent with vertebrates

Cephalopod Locomotion

• Five general types
• Jet propulsion
• Lateral fin undulation
• Lateral fin flapping
• Squid, some octopus
• Moderately fast, very efficient