Phylum Mollusca Chapter 12
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Transcript Phylum Mollusca Chapter 12
THREE MAIN CLASSES
1. Class Gastropoda
(snails, slugs, limpets)
2. Class Bivalvia (muscles,
clams, oysters)
3. Class Cephalopoda
(octopus, squid, nautilus,
cuttlefish)
Limpets
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
Protostomate
› Blastopore become mouth – ‘primitive’
Provides room for organ development
Surface diffusion of
› Gases
› Nutrients
› Wastes
Storage
Elimination of reproductive products
Hydrostatic support
Size: <1cm – 18m
› Garden slug – Giant squid
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
› Covers tonguelike structure
Snails, limpets, slugs
Over 35,000 species <Largest class>
Habitat: Marine, freshwater, terrestrial
Operculum ‘lid’
› Dorsal posterior end
› Used for protection from predators &
desiccation
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
Locomotion
› Flattened foot
Sometimes ciliated
Muscular contractions
› Cilia over mucous trail
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)
Cardiovascular:
› Open Circulatory System
Blood “hemolymph” leaves blood vessels
Blood bathes tissue directly in hemocoel ‘sinus’
› Function of blood: transport nutrients, wastes,
& gasses
Respiration
› Gills
› Diffusion of O2 across mantle
Digestion
› Food trapped in mucus strings
Gets incorporated into protostyle
› Protostyle – rotating ‘mucoid mass’ in gut of
gastropod
› Radula
› Ciliated digestive tract
Excretory Waste Removal
› Wastes excreted through coelom from blood
› Aquatic – produce ammonia
› Terrestrial – produce uric acid (less toxic) –
conserves water
› Nepheridium – excretory organ
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
Tongue &
grooves in shell
to prevent
twisting
Umbo – swollen
area – looks like
a notch
› Oldest part of
shell
Sheet like mantle
Muscular movement:
Adductor muscles
to close shell
› Defense against
predation
Sea stars can break
this muscle
Steaming bivalves…
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
Statocysts –
balance/gravity
Osphraidium –
chemoreceptors in
mantle
Cardiovascular System
› Open circulatory system
› Blood flow:
› heart tissue sinuses nepheridia gills
heart
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
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
Some internal fertilization
(fresh water only)
› Female sucks in sperm from
inhalent water
› Young clams shed from gills
Most complex mollusc
All except nautilus have a
reduced shell
› Cuttlefish & squid have
internal shell
› Nautilus has a coiled shell for
support
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