Mussel Dissection

Life Science, Mr. Ditolla

MollusksMany mollusks such as oysters, clams, and snails havehard outer shells. Other mollusks such as squids andoctopuses have rodlike supports within their bodies.Most mollusks live in the sea or in freshwater, but some species are found on land. Whether they havea shell or not, all mollusks have a soft body.

ShellThe mussel shell is made up of two sides, each side iscalled a valve. The valves are hinged together on oneside of the mussel, but can open along the other side.When the shell is closed, the valves are held togetherby two powerful muscles. You cannot open the shellwith your scissors so I will come around and open itwith a knife by cutting through both muscles.

valve

Shell StructureUsing the picture below, identify the parts of the shellon your mussel.

umbo

growth ring

hinge

Locate the thin mantle layer on the inner surface of eachvalve. This layer develops the shell and coats the shell’sinner surface. The space within the folds of the mantlelayer is the mantle cavity.

mantlemantle cavity

Locate the gills. The mussel breathes with its gills byremoving oxygen from the water.

gill

gill

Locate the muscle that I had to cut through to open yourmussel shell. This muscle contracts to close the shell. Some mussels have one of these muscles, others have two.

muscle

Using the tweezers, remove the mantle layer from oneof the valves. Notice the smooth, fine-grained innersurface of the valve. This shell lining is called themother-of-pearl.

remove this layermother-of

-pearl

A pearl is formed when a piece of sand or other irritant gets stuck in the mantle layer and irritatesthe mussel. The mussel then coats the irritant withmother-of-pearl, creating a pearl.

mantle layerpearl

Locate the two siphons. Water enters the mantle cavitythrough one siphon and passes out through the othersiphon. Mussels are filter feeders and filter out foodfrom the water as it is channeled through by the siphons.

siphon

siphon

Locate the large, muscular foot. When the mussel isalive the foot extends out through the shell and gripsthe stream bottom to slowly move the mussel along.

foot

Locate the body mass located under the foot.

body mass

Cut open the body mass and locate the digestive gland,which helps digest food, and the gonads, which produceegg and sperm cells.

Like other invertebrates, mussels do not have a back-bone. Mussels belong to the Mollusk phylum. Allmollusks have a soft body. Most mollusks have a shell,and most mollusks have a muscular foot.

Wipe your tools off, throw your mussel away, wipe outyour tray, and wash you hands with soap and water.

Answer the following questions on a separate pieceof paper.

Questions and Conclusions:1. Name three mollusks that have hard, outer shells.2. Name two mollusks that don’t have shells.3. Do any mollusks live on land?4. All mollusks have a soft __________.5. What is each side of the shell called?6. What do the muscles in the shell do ?7. What does the mantle layer do?8. What is the mantle cavity?9. How do mussels breath?10. What is the mother-of-pearl?11. How are pearls formed?*more questions on next slide

12. What do the siphons do?13. How do mussels obtain food?14. What is the function of the foot?15. What structure is located under the foot?16. What organs are located inside the body mass?17. What is the function of the digestive glands?18. What do the gonads do?19. Why are mussels classified as invertebrates?20. What phylum do mussels belong to?21. Most mollusks have a __________ and a muscular _________.22. All mollusks have a _______ body.