Mollusks Invertebrates

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MollusksInvertebrates
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Mollusks
Chart-notes

• Examples snails, slugs, clams, squid, octopus,
  oysters, scallops
• Phylum Mollusca soft-bodied
• Germ Layers 3
• Body Symmetry/shape Bilateral
• Segmentation none
• Coelom True Coelom
• Nervous some simple some complex
• Skeleton some hydrostatic some Exoskeleton
  (shells)

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The Mollusk Body Plan
Visceral mass-organs Shell-protection
Squid
Snail
Shell Mantle cavity Foot Gills Digestive tract
Clam
Earlymollusk
Foot- movement Mantle-thin membrane surrounding
organs
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Mollusks

• Digestion varies herbivores, carnivores,
  filter feeders, detritivores, or parasites
• Excretion tube-shaped nephridia
• Circulation some have open system, some have
  closed open- sinuses, simple vessels, simple
  heart
• Closed- complex blood vessels, complex heart
• Respiration aquatic-gills land-moist mantle
• Reproduction all sexual some hermaphrodites
• a. Internal Fertilization- eggs fertilized
  inside
• b. External Fertilization- eggs fertilized
  outside

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3 Classes of Mollusks

1. Class Gastropoda stomach foot
2. Class Bivalvia two shells
3. Class Cephalopoda head foot

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1. Class Gastropoda stomach-foot

• Shell-less or single shelled
• Examples
• snails, slugs, sea slugs
• Body Processes
• a. Digestion
• - radula tongue-like organ
• - teeth to scrape cut out food

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• Nervous System small brain
• Open Circulatory System
• Respiratory gills(aquatic), primitive lung, or
  diffusion through skin(land)
• may secrete slime to help
• in movement and breathing

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Snail Exterior
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Sea Slugs
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2. Class Bivalvia two shells

• Bivalves have 2 shells held together by one or
  two powerful muscles
• Examples Clams, oysters, scallops, and mussels

oysters
clams
scallop
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• Body Processes
• Movement
• - mostly remain in one place (especially
  oysters)
• - clams use foot to burrow into sand
• - mussels use sticky thread to attach to
  rocks
• - scallops can move rapidly by flapping
  shells
• Digestion filter feeders

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1. Respiration filter oxygen from the water using
   gills
2. Circulation open
3. Reproduction sexual, hermaphrodites

siphons
foot
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3. Class Cephalopoda head foot

• most complex/ most active mollusk
• head attached to foot that is divided up into
  tentacles
• Examples octopus, squid, cuttlefish, nautilus

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Body Processes of Cephalopods

• Digestion
• - radula sharp beak-like jaws
• - tentacles with suckers- capture prey/movement
• these adaptations make them effective marine
  predators
• Respiration gills
• Circulation closed circulatory system

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• Reproduction sexual
• - separate sexes
• - internal fertilization eggs put outside of
  body
• Nervous System
• - large brain
• - good eyesight
• - tentacles very sensitive to touch

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• Movement
• - jet propulsion squirts water out of siphons
  (holes in the side of the head)
• Defense
• - can change colors
• (used for camouflage communication)
• - can expel ink if threatened