Phylum: Mollusca

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Phylum Mollusca

• Gastropods, Bivalves Cephalopods

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Mollusks

• Mollusks are soft-bodied animals that usually
  have an internal or external shell.
• Ex. Clams, squid, octopi, mussels, nudibranchs.
• They have a free swimming larval stage called a
  trochophore.

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Body Plan 4 parts

• 1. foot used for crawling, burrowing and
  tentacles
• 2. mantle thin layer of tissue that covers
  organs
• 3. shell made by glands in the mantle that
  secrete calcium carbonate
• 4. visceral mass guts. (internal organs)

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Feeding

• Feeding radula ribbon of teeth
• Others are filter feeders using an incurrent and
  excurrent siphon

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Respiration and Circulation

• Respiration gills
• Circulation - Open circulatory system heart
  and open sinuses. Open works for slow moving
  creatures
• Closed circulatory system blood is contained in
  veins and arteries. Octopi and squid

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Response/Movement/Reproduction

• Response- Clams- simple nervous system/eyespot
• Octopi brains, complex behavior. Octopi and
  squid can open jars for reward or to avoid
  punishment
• Movement mucus with the foot/muscle or jet
  propulsion for the octopus.
• Reproduction usually external fertilization in
  the water. Some tentacled mollusks do internal
  fertilization. Some can be hermaphrodites.

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3 main groups of Mollusks

• 1. Gastropods shell-less or single shelled
  mollusks that move by using a muscular foot.
• Ex. Sea hares can squirt ink at
  predators
• Nudibranches sea slugs, have chemicals in
  their bodies that taste bad. Can recycle
  nematocysts from cnidarians they eat.

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3 main groups of Mollusks

• 2. Bivalves two shells held together by two
  powerful muscles.
• Ex. Clams, oysters, mussels and scallops.
  Scallops can flap their shells to move when
  threatened. Filter water over gills use mucus
  and cilia on gills to trap food particles.

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3 Main Groups of Mollusks

• 3. Cephalopods head-footed . Soft bodied.
  The head is attached to a single foot. The foot
  is divided into tentacles or arms.
• Example squid, octopus, nautilus, cuttlefish.
  They move by jet propulsion. Many have an ink
  sac to distract potential predators.
• They have a pen for a backbone.