Phylum Mollusca

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Phylum Mollusca
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Phylum level Characteristics

• soft-bodied with single muscular foot
• internal or external limestone shell
• complete digestive system
• coelomates
• grouped together because of similar developmental
  patterns
• live everywhere
• ocean, freshwater, on land

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General Body Plan

• Foot
• Mantle
• tissue that hangs or covers some or all of the
  body
• Shell
• hard structure can be internal or external
• Visceral mass
• contains all internal organs
• Radula
• unique to mollusks
• its a rasping organ with file like teeth to
  scrape, crush food
• Gills
• to extract oxygen from water and can filter food

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Feeding

• Every form of feeding is represented by the
  various types of mollusks
• Some utilize a radula
• Herbivores use it to scrape algae off surfaces
• Carnivores us it to drill into the shells of prey
• Octopi and sea slugs produce poison to subdue
  prey then use sharp jaws to eat them
• Filter feeders use gills to sift food from the
  water
• slug video

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Respiration

• Aquatic species use gills (found within the
  mantle cavity) to extract dissolved oxygen from
  the water
• Land molluscs breathe via an adapted mantle
  cavity lined with blood vessels. Must be kept
  moist for oxygen to enter the cells

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Circulatory System

• Slow moving or sessile species have an open
  circulatory system
• Blood not always within blood vessels
• Works through body tissues in open spaces called
  sinuses
• Faster movies species (like octopi) have a closed
  circulatory system
• Blood always within vessels
• More efficient

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Excretory System

• Complete digestive system
• Solid waste expelled through anus
• Metabolic wastes (ammonia) excreted by nephridia
  (simple kidney like organs)
• Nephridia remove wastes and excrete to outside
  through skin

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Nervous System

• Varies greatly between species
• Bi-valves have extremely simple systems
  consisting of a couple ganglia, nerve chords and
  sense organs
• Octopi and other complex molluscs have developed
  brains with memory and learning capacity

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Reproduction

• Again, varies between species
• Most have separate sexes and fertilization is
  external (in open water)
• More complex species have internal fertilization

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Ecological Economic Importance

• clams, oysters, scallops all farmed or fished for
  food
• octopus some food value, recreational diving to
  observe

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3 Main Classes

• Take some time to read over pages 590 592 to
  learn about the
• Gastropods
• Bivalves
• Cephalopods
• Complete Phylum Mollusca handout

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Squid External View
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Squid Internal Anatomy
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Assignment

1. Complete Phylum Mollusca handout from last class
2. With your partner, read over the handout for
   tomorrows dissection
3. Begin to fill in as much of the handout as you
   can.