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Biology 320 Invertebrate Zoology Fall 2005. Chapter 12 – Phylum Mollusca Part Three. Class Cephalopoda. 700 extant spp. described Nautiloids, cuttlefish, squids, and octopods Carnivores Fast swimmers that compete with fish Some anatomical / physiological similarities Ecologically similar

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biology 320 invertebrate zoology fall 2005

Biology 320Invertebrate ZoologyFall 2005

Chapter 12 – Phylum Mollusca Part Three

class cephalopoda
Class Cephalopoda
  • 700 extant spp. described
  • Nautiloids, cuttlefish, squids, and octopods
  • Carnivores
  • Fast swimmers that compete with fish
    • Some anatomical / physiological similarities
    • Ecologically similar
  • Most active molluscs
The largest invertebrates
    • Architeuthis – 20 m
    • Enteroctopus – 9.6 m arm span
  • Possibly the most intelligent invertebrates
    • Highly developed nervous system
    • Image forming eyes
    • Capable of complex behaviors
body form
Body Form
  • Dorsoventral axis of early molluscs elongated
  • Functionally, the ventral aspect of the cephalopods is really the anterior aspect
  • Head and foot are located at the anterior end
    • The name cephalopod means “head foot”
  • Houses brain (more later)
  • Mouth
  • Buccal cavity
    • Beak
    • Buccal mass
    • Radula
  • Anterior gut
foot and visceral mass
Foot and Visceral Mass
  • Foot is modified to form several appendages that surround the mouth
    • Arms
    • Tentacles
  • Ventral region of foot also forms tubular siphon (funnel)
    • Leads to mantle cavity
  • Visceral Mass
    • Dorsal
    • Elongate
    • Hump shaped
  • Thick and muscular
  • Surrounds visceral mass and mantle cavity
  • Mantle cavity is ventral / anterior; houses:
    • One or two pairs of bipectinate, nonciliated gills
    • Anus w/ ink sac attached
      • Releases ink which quickly forms a cloud
      • Confuses predators and can anesthetize chemoreceptors
    • Nephridiopore
    • Gonopore
  • External in nautiloids
  • Internal in squids and cuttlefish
      • Gladius or pen
      • Cuttlebone, respectively
  • Absent in octopods
buoyancy regulation
Buoyancy Regulation
  • Nautilus uses its shell
    • Chambers are filled with fluid and then septum forms
    • Gas / water can be pumped in / out of chambers
  • Those without shell use other methods
    • Replace high molecular weight sea water in coelom with low molecular weight ammonium ions
    • Lack of heavy external shell makes buoyancy less of a problem
    • Webbed octopods extend arms to increase SA and retard sinking
      • Web acts like a parachute
  • Important for:
    • Prey capture
    • Buoyancy regulation
    • Diel vertical migration (DVM)
  • Two main types
    • Crawling
    • Swimming
  • Crawling
    • Typical of octopods
Locomotion cont…
  • Swimming
    • Bell swimming in webbed octopods
    • Undulations of lateral fins
    • Jet propulsion by ejecting water from mantle cavity
      • Circular muscle contractions
      • Water ejected through exhalant siphon
      • Valve covers inhalant siphon
      • Propelled in opposite direction
      • Slow and fast jetting
      • Flying squids can fly 50 m through air
  • Cephalopods are visual predators, so they posses image forming eyes for prey detection (more later)
  • Raptorial
  • Capture using appendages, many of which are covered with suckers
    • May be toothed
  • Tentacles capture and arms manipulate in most cases
  • Beak is made of proteins and chitin
  • Buccal mass is large collection of muscles surrounding beak
Radula pulls in pieces of prey that the beak rips off
  • Many have venom glands that empty into buccal cavity
    • Venom and other secretions enter prey’s blood stream through beak wounds
  • Tetrodotoxin from little blue-ringed octopus is responsible for some human deaths
gas exchange
Gas Exchange
  • Considered to be concurrent in most cases
  • Ways to supplement gas exchange
    • Large gill SA
    • Some gas exchange across body surface
    • Rapid ventilation
    • Pressurized circulatory system
    • Restricted to cold water, which has higher O2 solubility
  • Closed system
  • Capillary beds are main sites of diffusion, as opposed to hemocoels
  • Hearts
    • One systemic - body
    • Two branchial - gills
  • Vessels lined with endothelium, as in verts
  • Hemocyanin
  • Ammonotelic
  • Two nephridia in all but nautiloids (which have four)
  • Nephridia are attached to pericardial cavity of branchial hearts
nervous system
Nervous System
  • Most developed of all inverts, and even rivals some verts
  • Cephalized and bilaterally symmetrical
  • Many ganglia and nerves
    • Some brains are enclosed in a cartilaginous cranium
  • Giant motor neurons for rapid transmission of impulses
  • Image forming eyes
    • Structurally similar to human eye
    • Cannot see in color
    • Can discriminate objects as small as 0.5 cm from 1 m away
Other sensory organs
    • Epidermal hair lines
      • Analogous to lateral lines of fish
      • Sensitive to water movement and pressure changes
    • Statocysts
    • Chemoreceptors
      • For taste or smell
      • May be located on suckers and tentacles
    • All except nautiloids lack osphradia
  • Organs with pigment cells located in dermis
    • Cells contain pigment sacs that are under nervous / muscular control
    • Sacs stretch out and flatten, causing pigment to spread out
    • Used for camouflage or when animal is alarmed
    • Some produce waves of color when making defensive displays
  • Also produce bioluminescence
  • Gonochoric
  • Single Gonad
  • Usually copulate but have indirect fertilization
    • Sperm is transferred in form of spermatophore
    • Male often transfers with modified arm known as a hectocotylus
  • Fertilization may be external (sea or mantle cavity) or internal
  • Often have courtship displays
Lay large (15mm) yolky eggs with gelatinous capsule
    • Can be free floating or attached
  • Many adults ventilate eggs while brooding
  • Some have direct development
  • Most adults have short lifespan (less than three years) and die after spawning
  • Four species of Nautilus
  • Found in the Indo-Pacific ocean
    • Typically between 100 m – 600 m
  • External shell that they can retract into
    • Leathery hood that acts like an operculum
    • Lack ink sack
    • Lack chromatophores
  • 90 arms
    • Some are mechanosensory and chemosensory
    • Lack suckers
Swim backwards
  • Specialize on decapods, especially hermit crabs
  • Two pairs of gills
  • Have osphradia
  • Slightly different circulatory system
    • Not entirely closed
    • No branchial hearts
    • Four nephridia
  • Sepia is a common genus
  • Not as fast or streamlined as squids
  • Eight arms and two tentacles
  • Swim over ocean bottom feeding on shrimps and crabs
  • Two gills
  • Loligo is a common genus
  • Can obtain greatest swimming speeds of any aquatic invert
    • 40 km / hr
  • Feed on fish, crustaceans, and other squids
  • Two gills
  • Eight arms and two tentacles
One of their main predators is the sperm whale
    • Sperm whales reach 20 m in length
    • 14,000 beaks found in the belly of one sperm whale
  • Giant squids
    • Architeuthis
    • Live at depths between 300 m and 600 m
    • Not rapid swimmers
    • Sucker scars found on sperm whales
  • Octopus is a common genus
  • Two gills
  • Tend to be benthic; often crawl over substrate
  • Typically live in a den
    • Leave to forage
    • Den usually littered with shells of prey items
  • Eight arms; no tentacles
  • Eat a variety of prey items, but clams, snails, and crustaceans dominate
Pacific giant octopus
    • Enteroctopus
    • Forages up to 250 m from den
    • Paralyze prey with venom and take back to den
    • Inject with poison and enzymes
    • Some drill holes through shells with radula
    • Feeding ecology is similar to that of spiders