Phylum Mollusca

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Phylum Mollusca
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Objectives for this set of notes

• Identify the major classes found under phylum
  Mollusca.
• Identify at least one animal from each class.
• Identify the characteristics that place these
  creatures the phylum Mollusca
• Identify the symmetry

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How do they fit into this Phylum?

• They share the following characteristics.
• 1. They have bilateral symmetry (divide into two
  equal planes)
• 2. Epithelial cells produce mucous
• 3. Body short and enclosed in a mantle that
  secretes a shell of 1, 2, or 8 parts
• 4. Digestive tract is complete Mouth to Anus
• 5. Have teeth like structures used to rasp at
  food (radula)
• 6. Has a circulatory system with a dorsal heart
  with 1 or two auricles and a ventricle
• Continued next page

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• 7. Respiration by 1 to many gills (ctenidia) or
  a lung
• 8. Has kidney like structures called nephridia
  that remove waste
• 9. Has a simple nervous system with 3 pairs of
  ganglia (mass of nerve cells) one above the
  mouth, one in the foot, and one in the viscera or
  body.
• 10. Sexes are usually separate. Some are
  hermaphroditic. No asexual reproduction

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Major Classes and animals found in each

• 1. Class Polyplacophora This is the chitons
  class. They are the most primitive mollusca.
• 2. Class Gastropoda Name means stomach foot.
  They all have a single foot with a shell on the
  back. Snails, limpets, nudibranchs (sea slugs)
  and abalones are a few examples.
• 3. Class Bivalvia Often classed bivalves (shells
  also called valves) Clams, oysters, and scallops
  are examples from this class.

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• 4. Class Cephalopoda Translates to head foot.
  Octopus and squid are examples from class
  cephalopoda.
• 5. Class Scaphopoda Tooth shells belong to
  this class. They live in the sand and their
  shells wash up on the beaches. They look like
  long teeth. They do not have a heart, or gills,
  but they do have a shell, radula, and mantle used
  to make the shell so they are still placed under
  the Phylum Mollusca.