Transcript Biology 320 Invertebrate Zoology Fall 2005

Biology 320
Invertebrate Zoology
Fall 2005
Chapter 12 – Phylum Mollusca
Part Three
Class Cephalopoda

700 extant spp. described

Nautiloids, cuttlefish, squids, and
octopods
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Carnivores
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Fast swimmers that compete with
fish
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

Some anatomical / physiological
similarities
Ecologically similar
Most active molluscs
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The largest
invertebrates
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

Architeuthis – 20 m
Enteroctopus – 9.6 m
arm span
Possibly the most
intelligent
invertebrates
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
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Highly developed
nervous system
Image forming eyes
Capable of complex
behaviors
Body Form

Dorsoventral axis of early
molluscs elongated
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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”
Head

Houses brain (more later)
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Mouth
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Buccal cavity
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Beak
Buccal mass
Radula
Anterior gut
Foot and Visceral Mass

Foot is modified to form
several appendages that
surround the mouth

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
Ventral region of foot also
forms tubular siphon (funnel)

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Arms
Tentacles
Leads to mantle cavity
Visceral Mass
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Dorsal
Elongate
Hump shaped
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Thick and muscular
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Surrounds visceral mass and
mantle cavity
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Mantle cavity is ventral /
anterior; houses:

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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
Mantle
Shell

External in nautiloids
 Internal in squids and cuttlefish
• Gladius or pen
• Cuttlebone, respectively

Absent in octopods
Buoyancy Regulation

Nautilus uses its shell

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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
Locomotion
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Important for:

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
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Two main types

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
Prey capture
Buoyancy regulation
Diel vertical migration
(DVM)
Crawling
Swimming
Crawling

Typical of octopods

Locomotion cont…
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Swimming
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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
Nutrition
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Cephalopods are visual predators,
so they posses image forming
eyes for prey detection (more
later)
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Raptorial
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Capture using appendages, many
of which are covered with suckers
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May be toothed
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Tentacles capture and arms
manipulate in most cases
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Beak is made of proteins and
chitin
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Buccal mass is large collection of
muscles surrounding beak
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Radula pulls in pieces of
prey that the beak rips off
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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
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Considered to be
concurrent in most cases
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Ways to supplement gas
exchange
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Large gill SA
Some gas exchange
across body surface
Rapid ventilation
Pressurized circulatory
system
Restricted to cold water,
which has higher O2
solubility
Circulation

Closed system
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Capillary beds are main sites
of diffusion, as opposed to
hemocoels
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Hearts
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One systemic - body
Two branchial - gills
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Vessels lined with
endothelium, as in verts
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Hemocyanin
Excretion
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Ammonotelic
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Two nephridia in all
but nautiloids (which
have four)
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Nephridia are
attached to pericardial
cavity of branchial
hearts
Nervous System
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Most developed of all inverts, and even
rivals some verts
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Cephalized and bilaterally symmetrical
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Many ganglia and nerves

Some brains are enclosed in a
cartilaginous cranium
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Giant motor neurons for rapid
transmission of impulses
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Image forming eyes

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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
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Statocysts
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Chemoreceptors
• For taste or smell
• May be located on suckers and tentacles
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All except nautiloids lack osphradia
Chromatophores
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Organs with pigment cells
located in dermis
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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
Reproduction
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Gonochoric
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Single Gonad
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Usually copulate but have indirect fertilization
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Sperm is transferred in form of spermatophore
Male often transfers with modified arm known as a hectocotylus
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Fertilization may be external (sea or mantle cavity) or
internal
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Often have courtship displays
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Lay large (15mm) yolky
eggs with gelatinous
capsule
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Can be free floating or
attached
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Many adults ventilate
eggs while brooding
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Some have direct
development
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Most adults have short
lifespan (less than three
years) and die after
spawning
Nautiloids
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Four species of Nautilus
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Found in the Indo-Pacific ocean
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External shell that they can
retract into
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Typically between 100 m – 600 m
Leathery hood that acts like an
operculum
Lack ink sack
Lack chromatophores
90 arms
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Some are mechanosensory and
chemosensory
Lack suckers
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Swim backwards
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Specialize on decapods, especially hermit crabs
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Two pairs of gills
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Have osphradia
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Slightly different circulatory system
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Not entirely closed
No branchial hearts
Four nephridia
Cuttlefish
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Sepia is a common genus
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Not as fast or streamlined
as squids
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Eight arms and two
tentacles
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Swim over ocean bottom
feeding on shrimps and
crabs
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Two gills
Squids
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Loligo is a common genus
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Can obtain greatest
swimming speeds of any
aquatic invert
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40 km / hr
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Feed on fish, crustaceans,
and other squids
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Two gills
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Eight arms and two
tentacles
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One of their main
predators is the sperm
whale
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Sperm whales reach 20 m
in length
14,000 beaks found in the
belly of one sperm whale
Giant squids
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Architeuthis
Live at depths between 300
m and 600 m
Not rapid swimmers
Sucker scars found on
sperm whales
Octopods
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Octopus is a common genus
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Two gills
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Tend to be benthic; often crawl
over substrate
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Typically live in a den
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Leave to forage
Den usually littered with shells of
prey items
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Eight arms; no tentacles
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Eat a variety of prey items, but
clams, snails, and crustaceans
dominate
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Pacific giant octopus
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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