13'1 mollusks

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13.1 mollusks
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Characteristics of Mollusks

• Soft bodied, invertebrates with bilateral
  symmetry.
• Most live in water, few live on land.
• More than 110,000 species identified and named.

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Body Plan

• Mantle is a thin layer of tissue than covers the
  organs and secretes the shell.
• Mantle cavity is the space between the shell and
  visceral mass (body) than contain gills.
• Open circulatory system heart pumps blood into an
  open area around the organs.

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Body Plan II

• Mollusks have well developed head with mouth and
  sensory organs.
• Mollusk shells have several layers, the inside
  layer is the smoothest and thickest.

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Classification of Mollusks

• The first scientist look for a shell.
• If they have a shell they are divided by the kind
  of shell.
• Three largest groups are gastropods, bivalves and
  cephalopods

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Gastropods

• The largest group of mollusks most have a single
  shell.
• Have a radula, a file like tongue they use to
  scrape food.
• Eyes are on tentacles at the head region.
• Living on land requires adaptations to prevent
  water loss.

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Bivalves

• Bivalves have two hinged shells attached by
  strong muscles.
• Strong muscular foot to bury them selves in sand.
• Some can move by quickly contracting shell
  muscles.
• Some cement selves to one spot.

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Cephalopods

• Cephalopods are the most diverse and specialized.
• The word cephalopod means head footed, They have
  a large head and the foot is divided into
  tentacles.
• Are all predators
• Have closed circulatory system, blood in veins.
• Eyes and brains are well developed and large for
  body size.

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Cephalopod Propulsion

• Cephalopods are adapted for swimming.
• Many can force water out small nozzles to push
  its self trough the water. (Jet Propulsion)
• Can move very quickly over short distances.
• Jet propulsion is only used for short distances,
  many of them have other ways to move.

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Origin of mollusks

• Mollusk fossils date back 500 million years.
• Many of the mollusks went extinct 66 mya.