THREE MAIN CLASSES
1. Class Gastropoda
(snails, slugs, limpets)
2. Class Bivalvia (muscles,
clams, oysters)
3. Class Cephalopoda
(octopus, squid, nautilus,
cuttlefish)
Limpets
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Bilateral Symmetry
Invertebrate - no backbone
Hydrostatic Skeleton (fluid under pressure)
Triploblastic
Coelomate
› 1st animals to posses a coelom
 Yes, even before annelids…
› Small cavity; surrounds heart, nephridia, gonads
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Protostomate
› Blastopore become mouth – ‘primitive’
Provides room for organ development
 Surface diffusion of
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› Gases
› Nutrients
› Wastes
Storage
 Elimination of reproductive products
 Hydrostatic support
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Size: <1cm – 18m
› Garden slug – Giant squid
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3 Body Regions
› Mantle – tissue that covers the body
 May secret a shell
 Fxn: excretion, gas exchange, elimination of
wastes, reproductive products
› Visceral mass – contains organs
› Head foot – elongate foot w/ anterior head
Open circulatory system in all except
cephalopods
 Radula – rasping/scraping structure
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› Covers tonguelike structure
Snails, limpets, slugs
 Over 35,000 species <Largest class>
 Habitat: Marine, freshwater, terrestrial
 Operculum ‘lid’
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› Dorsal posterior end
› Used for protection from predators &
desiccation
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Undergo Torsion during larval stage› 180° Twist of visceral mass & mantle
 Allows head to enter shell first for protection
 Allows for clean water in front of the snail to
enter mantle cavity
 Makes snail more sensitive to stimuli coming
from the direction in which it moves
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Locomotion
› Flattened foot
 Sometimes ciliated
 Muscular contractions
› Cilia over mucous trail
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Nervous Communication
› Ospharidia
 Chemoreceptors
 Detect sediment & chemicals in inhalant H20
 Helps detect prey
› Ganglia linked by nerves
› Eyes @ base or end of tentacles
 Photo receptors
 Lens & Cornea
› Statocysts in the foot (balance)
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Cardiovascular:
› Open Circulatory System
 Blood “hemolymph” leaves blood vessels
 Blood bathes tissue directly in hemocoel ‘sinus’
› Function of blood: transport nutrients, wastes,
& gasses
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Respiration
› Gills
› Diffusion of O2 across mantle
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Digestion
› Food trapped in mucus strings
 Gets incorporated into protostyle
› Protostyle – rotating ‘mucoid mass’ in gut of
gastropod
› Radula
› Ciliated digestive tract
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Excretory Waste Removal
› Wastes excreted through coelom from blood
› Aquatic – produce ammonia
› Terrestrial – produce uric acid (less toxic) –
conserves water
› Nepheridium – excretory organ
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Reproduction
› Marine snails – external
fertilization
 Dioecious
 Gametes discharged into sea
› Freshwater & Terrestrial snails
– internal fertilization
 Monecious
 Copulation - Exchange sperm
– or  One snail may act as the male,
the other as the female
Mussels, clams, oysters,
scallops
 Habitat: Marine,
freshwater
 Help remove bacteria
from polluted water
 2 convex halvesvalves
 Proteinaceous hinge
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Tongue &
grooves in shell
to prevent
twisting
 Umbo – swollen
area – looks like
a notch
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› Oldest part of
shell
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Sheet like mantle
Muscular movement:
 Adductor muscles
to close shell
› Defense against
predation
 Sea stars can break
this muscle
 Steaming bivalves…
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Sessile (immobile)
Nervous Communication
 3 pairs of
interconnected ganglia
 Margin of the mantle is
main sense organ
› has sensory cells
› Tentacles
› Photo receptors or Lens &
Cornea
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Statocysts –
balance/gravity
Osphraidium –
chemoreceptors in
mantle
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Cardiovascular System
› Open circulatory system
› Blood flow:
› heart  tissue sinuses  nepheridia  gills 
heart
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Respiration
› Gills covered in cillia
› diffusion
Digestive System
 Filter feeders
 Gills trap food
particles
 Move down
food grooves
(ciliated tracts)
 Labial palps sort
food particles
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Excretory System
› 2 Nepheridia
› Duct system
› Nephridiopores in
anterior region for
excretion of wastes
Reproduction
 Most dioecious –
male/female
 Few monoecous –
hermaphroditic
 Most external fertilization
› Spew out gametes and
fertilize in sea
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Some internal fertilization
(fresh water only)
› Female sucks in sperm from
inhalent water
› Young clams shed from gills
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Most complex mollusc
All except nautilus have a
reduced shell
› Cuttlefish & squid have
internal shell
› Nautilus has a coiled shell for
support
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Modified foot for food
capture, attachment,
locomotion, & reproduction
Visceral mass located in
head segment
Muscular movement
 Jet propulsion
 Foot modified into tentacles
Nervous Communication
 Highly developed nervous system
 Brains are large
 Fusion of ganglia
 Statocysts (gravity)
 Eyes
Cardiovascular
 1st to have Closed circulatory system
 Heart consists of 2 auricles and 1 ventricle
 Have contractile arteries and branchial hearts
Respiration
 Gills & diffusion
Digestive System
 Jaws & Radula
 Tentacles w/
adhesive cups or
foot to capture
prey
 Feed on small
invertebrates
 Efficient
predators