Classes of Molluscs: Cephalopoda

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Classes of Molluscs Cephalopoda

• C. Cephalopoda (squid/octopus/nautilus/devilfish/c
  uttlefish)
• 2 cm ? giant squid (largest invertebrate known)
• mostly marine
• octopuses mostly intertidal
• squids are deep-sea animals
• predators
• foot is in head region
• modified for expelling water from
  mantle cavity

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Classes of Molluscs Cephalopoda

• Major groups of cephalopods
• 3 subclasses of cephalopods
• Nautiloidea - 2 pairs of gills
• Ammonoidea - extinct
• Coleoidea - 1 pair of gills
• Nautilus only surviving genus in Nautiloidea that
  populated Paleozoic seas
• 5-6 living species
• head w/ 6090 tentacles that extend from opening
  of shell
• tentacles lack suckers, have adhesive secretions
• 4 O. of Coleoidea include all living cephalopods
  except Nautilus
• O. Sepioidea - cuttlefishes w/ round body, 8
  arms, 2 tentacles
• O. Myopsida and Oegopsida - squids w/ more
  cylindrical body, 8 arms, 2 tentacles
• O. Vampyromorpha - 1 sp. of deepwater vampire
  squid
• O. Octopoda - 8 arms, 0 tentacles

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Classes of Molluscs Cephalopoda

• Shell
• gas chambers in nautiloid and ammonoid shells
  allow swimming
• bouyancy
• nautilus shell divided into chambers
• living animal only inhabits the last chamber
• cord of tissue (siphuncle) connects chambers to
  visceral mass
• gas pressure in nautilus chambers 1 atm
  
• 41 atm in deep ocean

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Classes of Molluscs Cephalopoda

• cuttlefish shell enclosed in mantle
• squid shell is thin strip enclosed in mantle
  (pen)
• octopus has completely lost shell

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Classes of Molluscs Cephalopoda

• Locomotion
• swim by forcefully expelling water via ventral
  funnel/siphon
• octopuses crawl on bottom/swim backward by
  spurting water jets
• webbing btwn arms allows swimming w/ medusa-like
  action
• control direction/force of water
• determines speed
• lateral fins of squids/cuttlefishes stabilize
• Active life of cephalopods
  reflected in
  respiratory/
  circulatory/nervous systems

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Classes of Molluscs Cephalopoda

• Respiration/circulation
• 1 pair of gills
• 2 pair in Nautilus
• muscular pumping keeps water flowing through
  mantle cavity when ? O2 demand
• network of vessels conducting blood through gill
  filaments
• blood goes to
  systemic
  circulation
  before gills
• accessory/branchial
  ? at
  base of each
  gill ?
  pressure

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Classes of Molluscs Cephalopoda

• Nervous/sensory systems
• largest brain of any invertebrate
• giant nerve fibers
• well-developed sense organs
• complex eyes (cornea/lens/retina)
• learn by reward/punishment/ observation of others
• lack hearing
• tactile/chemoreceptor cells in arms

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Classes of Molluscs Cephalopoda

• Communication
• chemical/visual signals
• cells in skin contain pigment granules
  (chromatophores)
• contractions of muscle fibers attached to cell
  boundary cause cell to expand and change color
  pattern
• deep-water cephalopods have luminescent organs
• ink sac empties into rectum
• ink gland secretes sepia
  when
  animal is alarmed

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Classes of Molluscs Cephalopoda

• Reproduction
• dioecious
• ? seminal vesicle
• spermatozoa packaged in spermatophores and stored
• 1 arm of ? modified as intermittent organ
  (hectocotylus)
• plucks spermatophore from mantle cavity and
  inserts it into ?
• fertilized eggs leave oviduct, attach to
  substrate
• large, yolky eggs
• hatch into juveniles w/ no free-swimming
  larval stage

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