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Focus: Phylum Mollusca


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Biology 212

Focus: Phylum Mollusca



What will be turned in (beginning of next lab period)

  1. Sketches/descriptions of the mussel dissection (see separate handout for more detail).

  2. Worksheet comparing members of Class Gastropoda (limpet or keyhole limpet) and Class Polyplacophora (chiton).

  3. Essay: For each feature in the Gastropoda/Polyplacophora worksheet, explain the differences you see among all 4 classes based on how the animals are adapted to their particular environment and lifestyle. [For example, what is the significance of having 8 shell plates, instead of just one shell, for the chiton?]

  4. NOTE: The cephalopod dissection does not have an accompanying worksheet; however, you should examine it closely and learn key parts for the lab practical as well as include the cephalopod in your essay.




  1. Laboratory Objectives

    1. To become familiar with the key Molluscan characterisitcs.

    2. To view the key Molluscan characteristics for four Classes of Phylum Mollusca: Polyplacophora, Gastropoda, Bivalvia and Cephalopoda.

    3. To understand how the differences of the major Molluscan characteristics among the Classes is related to how members of the different classes are adapted to their environment.




  1. Methods




    1. Mussel dissection: See separate handout!



    1. Class Polyplacophora (chitons) and Class Gastropoda (limpets, snails and others): a comparison. Complete the worksheet!


NOTE: These are live animals and must be kept beneath the seawater at all times. You can turn them over, as this will help you see key features. You can also sometimes “persuade” them to stick their foot onto a slide, and then you can turn them over to observe their ventral surfaces.


      1. Be sure you closely examine at least one type of chiton (Class Polyplacophora) and one limpet (Class Gastropoda).

      2. Observe the key molluscan features in the live specimens available with the dissecting microscope, noting the similarities and differences for each of these two classes compared to HAM. You should attempt to observe each of the following features. Features with stars require some description in the worksheet.

        1. Diagrams of the ventral view of these molluscs have been provided to assist you with identification of parts; however, you should sketch and describe what you see in the actual animals and not simply copy the diagrams onto your worksheet! Note that for the most part, the actual animals, and not the diagrams, will be used for the lab practical.




Shell*

Head and associated sensory structures*

Mantle*

Radula

Mantle cavity*

Foot and epipodial tentacles*

Ctenidia*

Visceral mass (approximate location)




  1. Cephalopod dissection. Learn parts and genders for the lab practical!

    1. Introduction: The market squid, Loligo opalescens, are caught when they migrate from deeper water to the shallows in order to mate and lay their eggs.

      1. NOTE: It is possible that you will dissect a cephalopod other than Loligo.

    2. Initial dissection

      1. Cut the squid’s mantle open longitudinally, on the side opposite the pen. This will expose the mantle cavity.

    3. Identify the following parts of the squid. Be sure you look at both a male and a female squid. You may also identify more structures as indicated on the diagram if you have time, but the features listed below will be those that will be included on the practical. For starred items (*), know their structure of origin in HAM and think about how each is different from (or similar to) the “original” structure.

      1. Head*

      2. Arms* (8) and tentacles* (2)

      3. Mantle*

      4. Mantle cavity*

      5. Fin*

      6. Funnel (a.k.a. “siphon”)*

      7. Funnel retractor muscles

      8. Ink sac

      9. Ctenidia (a.k.a. “gills”)*

      10. Branchial (or ctenidial) hearts

      11. Main heart* (Think about circulatory system in cephalopods vs. others.)

      12. Ovaries (female)

      13. Nidamental glands: Find in the female; these put on the outer egg casing once the eggs are fertilized.

      14. Testes (male)

      15. Penis (male): You should be able to see spermatophores within the penis.

      16. Visceral mass

      17. Giant synapse and giant axons (I’ll point these out. We’ll talk about them in the neurobiology portion of the class.)

    4. Dissect the eye and find the lens. What shape is the lens?

    5. Dissect the head and find the beak. You might find the radula, but that is unlikely.

    6. Remove the pen*.

      1. Write your name in pen and ink on one of the handout pages.

    7. Quiz your partner on all parts, including location and corresponding structures in HAM where indicated.

Worksheet: Class Polyplacophora and Class Gastropoda. Complete the chart. You may use sketches, descriptions or both within the chart. The idea is to describe and to point out key differences from HAM. Use additional paper if needed!





Feature

Class Polyplacophora

Class Gastropoda

Shell






Mantle and associated structure (look for sensory tentacles at the edges)







Mantle cavity/ctenidia







Head and associated sensory structures (eyes, tentacles, etc…). Also comment on the mouth here.







Foot








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