Biology 320 Invertebrate Zoology Fall 2005

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Biology 320Invertebrate ZoologyFall 2005

• Chapter 12 Phylum Mollusca Part Three

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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

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• 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

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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

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Head

• Houses brain (more later)
• Mouth
• Buccal cavity
• Beak
• Buccal mass
• Radula
• Anterior gut

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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

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Mantle

• 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

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Shell

• External in nautiloids
• Internal in squids and cuttlefish
• Gladius or pen
• Cuttlebone, respectively
• Absent in octopods

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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

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Locomotion

• Important for
• Prey capture
• Buoyancy regulation
• Diel vertical migration (DVM)
• Two main types
• Crawling
• Swimming
• Crawling
• Typical of octopods

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• 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

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Nutrition

• 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

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• 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 preys blood
  stream through beak wounds
• Tetrodotoxin from little blue-ringed octopus is
  responsible for some human deaths

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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

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Circulation

• 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

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Excretion

• Ammonotelic
• Two nephridia in all but nautiloids (which have
  four)
• Nephridia are attached to pericardial cavity of
  branchial hearts

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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

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• 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

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Chromatophores

• 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

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Reproduction

• 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

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• 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

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Nautiloids

• 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

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• 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

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Cuttlefish

• 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

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Squids

• 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

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• 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

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Octopods

• 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

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• 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