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Mollusks : gastropods, bivlaves and cephalopods

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Mollusks : gastropods, bivlaves and cephalopods. Mollusks: Soft-bodied animals that usually have an internal or external shell. Common mollusks are snails, slugs, clams, squid and octopi. Mollusks have a free-swimming larvae called a trochophore. Mollusk Body Plan:

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gastropods, bivlaves and cephalopods



  • Soft-bodied animals that usually have an internal or external shell.
  • Common mollusks are snails, slugs, clams, squid and octopi.

Mollusk Body Plan:

  • Four basic parts shared by most mollusks:
  • Foot: Muscular structure used for different purposes: crawling, digging and catching prey.
  • 2. Mantle: Thin layer of tissue around the body.
  • 3. Shell: Made by glands in the mantle. The shell is missing in some mollusks (slugs.)
  • 4. Visceral Mass: All the organs.


Mollusks as a group eat all types of food.

Snails use a radula to scrape algae or drill into the shells of other mollusks.

Octopi and Squid use their jaws and sometimes poison to kll their prey.

Shellfish, like clams, are filter feeders. They use a siphon to bring in water and filter out the food.



Water mollusks use gills in their mantle cavity to breathe. Land mollusks use diffusion to get oxygen .


A heart pumps blood through an open or a closed circulatory system. Slow mollusks use an open system, while fast ones use a closed system.


The nervous systems range from simple in shellfish to complex in the well-developed brains of intelligent Octopi.


Some mollusks release eggs and sperm into the water, others mate and have internal fertilization.



-Have one shell or no shell at all, and crawl on a muscular foot on their ventral surface.

-Snails, slugs, limpets

-Shelled gastropods can hide inside their shells.

-Mollusks without shells either hide, squirt ink or contain poisons.



  • Have two shells held together with muscles
  • Clams, oysters, mussels, scallops
  • Most stay in one place, in the bottom or on rocks.
  • Most bivalves are filter-feeders, using their siphons to move water through their bodies.


-Soft-bodied mollusks, where the foot is divided into tentacles.

-Include octopi, squid, cuttlefish and nautiluses.

-Eight or more tentacles with sucking disks for holding prey.

-Most cephalopods only have a small internal shell (cuttlefish) or none at all. The nautiluses have an external shell.

-Complex eyes and brains make cephalopods intelligent hunters.