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Mollusks
  Phylum Mollusca
  Coelomates- have coelom
  More than 110,000 species
  Survive on land, fresh and marine waters.
Body Structure
  Bilateral symmetry
  Soft internal body
  Digestive tract, respiratory system,
circulatory system and nervous system.
  Have a mantle; which is a membrane that
surrounds the internal organs or mollusks.
  Mantle can secrete calcium carbonate to form a
shell.
Body structure
Feeding and digestion
  Can be herbivorous, carnivorous or filter
feeders.
  Radula- tonguelike organ with rows of teeth.
  Radula is used for scraping algae off rocks
or to drill into other animals to feed on
internal body parts.
  Have two openings to digestive tract.
  Have stomach and intestine
Respiration
  Most mollusks have gills
  Gills- parts of the mantle that consist of a
system of filamentous projections.
  used to transport oxygen into and to remove
carbon dioxide from the blood.
  Move water through the mantle
  Increase surface area for gas diffusion
  Land snails and slugs take in oxygen using
mantle cavities.
Circulation
  Have a chambered heart
  Most mollusks have a open circulatory system
  Blood is pumped to open spaces surrounding body
organs
  Utilized by slow moving animals (snails, slugs)
  Some mollusks have closed circulatory system
  Blood is confined to vessels as it moves through body
  Used by animals that move quickly (squid and
octopus)
Excretion
  Most mollusks get rid of metabolic waste through
the nephridia.
  Nephridia- maintains homeostasis in body fluids.
Response to stimuli
  Have nervous system that coordinates movement
and behavior.
  Octopus have a brain and a complex eye.
Movement
  Muscular foot is used for movement
movement
  Squid and octopus use a siphon to move water into
and then expel it out of the mantle.
Reproduction
  Reproduce sexually
  Most release eggs and sperm into water at the
same time. (external fertilization)
  Hermaphroditic mollusks use internal fertilization.
  All mollusks have a larval stage called a
trochophore.
Gastropods (Gastropoda)
  Stomach-footed mollusks
  Most have single shell
  Aquatic and moist terrestrial habitats
  Can draw their bodies into their shell when
threatened.
  Slugs secrete mucus for protection
  Nudibranchs incorporate jellyfish nematocysts into
their bodies after eating them; for protection
  Ex: snails, conches, periwinkles, limpets, cones.
Bivalves (Bivalvia)
  Two shelled mollusks
  Most are marine
  Few found in freshwater
  Continuously filter feeding
  Ex: clams, mussels, oysters and scallops
Cephalopods (Cephalopoda)
  Head-footed mollusks
  Foot is divided into arms and tentacles
  Have suckers; used to capture prey
  Most can expel ink when threatened
  Shells:
  Nautilus has external shell
  Squid and cuttlefish have internal shell
  Octopus has no shell
  Octopuses, squid and cuttlefish can change color
for camouflage
  Nautilus can hide in its shell when threatened.