Archerd Shell Collection > Shell Classes > Self Study Guide


Molluscs — An Introductory Self Study

(print this document and use for guide)

 

1.  At home, open the web to <http://shells.tricity.wsu.edu>

In computer lab, after login go to Start/ Explorer, close any popup screens; then in the Explorer window, open the web on <shells.tricity.wsu.edu>  (the http:// prefix may not be needed, here).

 

2.  Navigate to Gladys Archerd Shell Collection.

Click on the Shell Classes & Families button, and notice the underwater picture of Cymbiolacca pulchra wisemani (Brazier, 1870), a marine gastropod living on the Australian reef. Note the brilliantly patterned, widespread gliding foot that this animal uses for moving across the sea floor. It can creep up and smother a smaller creature, which is its principal mode of feeding.

 

3.  Click, next, on the picture above (or The Five Principal Classes button, at bottom of page).Read  Overview of the Phylum Mollusca. Note especially the main features of gastropod (snail) versus bivalve species. Detailed information links are shown in red text. For questions, 4-7, work from this page as your home page and check out the links (in red).

   a.  In the gastropod class, compared to the bivalve class generally, what is the principal type of food?

   b.  Are there any exceptions, in this regard?

4.  Return to the Overview page above.

   a.  What kind of body plan is the gastropod based on?

   b. How has it changed from early ancestral form to present day forms?

   c.  Click on the nervous system link. Compare the Patellogastropod nervous system with the Neogastropod nervous system. What is the consistent trend of Neogastropod nervous systems.

     d.  Click on the several links and compare Chiton, Pecten, and Strombus eyes. Eyes show a great range of histological differences.  Which do you think is the most evolutionarily advanced mollusc? Is your decision based solely don histological differences or are other systems involved?

   e.  Click on the Radula link. The radula is a hardened cartilaginous "tongue" that is usually preserved fairly well in dead specimens. Examine the differences between the two major orders of the Prosobranchia, namely Patellogastropoda versus Neogastropoda (“recent” snails). Why are the radulas so different between these two species of limpet?

5.  Return to The Five Principal Classes page. Now click on the Gastropoda (snails) picture  [a Murex species is pictured]. This brings you to the Index of Families in the gastropod class, fifty-six of which are listed here. The Family, or sometimes the Superfamily, is the basic unit of reference in studying these highly diverse creatures. Spend some time examining the following pairs of families.

a. How does the mode of protection against predators differ within each pair of the following three families? 

    i.  Cypraeidae (cowrie) vs.  Strombidae (conch)

    ii. Terebridae vs. Turritellidae

   iii.  Harpidae vs. Hydatinidae (or Bullidae)  

6.  Return to the Gastropod Family Index page and click on the link, Classification System. Notice that the taxonomic table (zoological systematics) is not  organized alphabetically. Is there any pattern to the organization of the tables?

 7.   Again, return to the Gastropod Family Index page. Now, click on and examine the Subclass Prosobranchia with the Informal Group Opisthobranchia (formerly, a subclass)

     a.  What distinctive anatomical features generally separate the two?

     b.  Return to the Gastropod Family Index. Pulmonates are generally air-breathing snails, common on land. For a long time, they were connsidered to be a subclass, which is now considered to be inappropriate as a phylogenetic classification. What clades currently include pulmonate species? Are they foundonly among the land snalils

 

8.   Take a few moments to familiarize yourself with the various families of gastropod mollucscs. Also take time to see living gastropod molluscs where we have links to underwater photos.

9.   Return to the Gastropod Family Index page. Use the Family buttons, and specifically compare information about the two Vetigastropoda families, Pleurotomariidae and Haliotidae (abalone), against information on the two Neogastropoda families, Muricidae and Conidae.

a. What are the criteria for thinking the Neogastropoda clade is more specialized than the Vetigastropoda clade?

b. Using  the Family buttons, specifically compare information about the Turbinellidae shells and the Terebridae which look very much alike. They show similar color and marking, but details of the aperture are distinctive.

      (i)  How is the life style of the Turbinellidae mollusc different from the life style of the Terebridae mollusc?

      (ii)  From a Darwinian viewpoint, why do you think the shells of the Turbinellidae are so similar to shells of the Terebridae?


Optional further items

10. Now return to the Five Principal Classes page. Click on the bivalve picture [a scallop].Then, on the Bivalve Family Index page, click on the Tellinidae family. Two strikingly different tellin clam shells are shown, one very thin and paper-like; the other heavy and quite solid . What is the difference in habitats that each of these two species occupy?

 

      (Hint: The thin tellin clam is a lot like the razor clam shown on the Cultellidae family page)

 

11. Compare organ systems for gastropods versus bivalves.

      a.  What different organ does the bivalve principally depend on for feeding?

      b.     Among the bivalves, are there any exceptions to this feeding mechanism?

 

12. Return to the Bivalve Family Index page, and examine information for both the Cardiidae (cockle) and Pectinidae (scallop) families.

      a.  What do you think are the main differences in habitat for these two families?

     b.  Why do you think the cockle shells are so ponderous compared to the delicate scallop shells?

 

13. Should we consider bivalves, in general, to be more or less primitive (ancestrally) compared to the gastropoda class? Why or why not? Please explain.