Archerd Shell Collection > Shell Classes > Self Study Guide
(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> (DON'T use the http:// prefix, here
2. Navigate to Gladys Archerd Shell Collection/Shell Collection. Click on the Shell Classes & Families button, and bring up the underwater picture of a living marine gastropod on the Australian reef. Now click on The Five Principal Classes button.
3. On the Five Principal Classes 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 home and check out the links.
4. Is it true that carnivorous molluscs are found only among the gastropod class? Does any other class of mollusc have a carnivorous species?
5. What kind of body plan is the gastropod based on, and how has it been changed by torsion?
6. Eyes are generally considered a feature of evolutionarily advanced specialization. Click on the links and compare Chiton, Pecten, and Strombus eyes. Among these very different molluscs, which do you think is the most evolutionarily advanced mollusc? Why?
7. 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 Archaeogastropoda (“ancient” snails) versus Caenogastropoda (“recent” snails). What does the radula tell about the lifestyle of the mollusc it came from?
8. 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. Spend some time examining the following pairs of families:
• Cypraeidae (cowrie) vs. Strombidae (conch)
• Terebridae vs. Turritellidae
• Harpidae vs. Hydatinidae or Bullidae
How does the mode of protection against predators differ among each of these pairs?
Follow links and take a few moments to see pictures of some of the live molluscs
9. Return to the Gastropod Index Page and click on the link, "System Classification." Notice that the taxonomic tables (zoological systematics) are not organized alphabetically. Why do you think the standard taxonomic table is not portrayed alphabeically? Is there a definite pattern to the organization of the tables? (Hint: What does the prefix “Archaeo-” mean as compared to “Caeno-”
10. Return to Gastropod Index Page. Now, examine the subclasses, Prosobranchia, Opisthobranchia, and Pulmonata. What distinctive anatomical features generally separate these subclasses (described earlier)? What is unique about the subclass, Pulmonata?
11. Compare the Archaeogastropods with the Caenogastropods. What is a hallmark of the Caenogastropod nervous systems
12. Click on the red colored links, and specifically compare information about the Pleurotomariidae and Haliotidae (abalone) families against information on the Caenogastropoda families, namely Muricidae and Conidae. What are the criteria for thinking one is more specialized than the other?
13. Compare the shells of the Terebridae family with shells of the Melongenidae family. Why do you think the Terebridae have evolved such a markedly corkscrew-shaped shell?
14. The Turbinellidae shells look substantially like the shells of the Terebridae family. They even show similar color and markings, although details of the aperture are distinctiuve. Nevertheless, the Turbinellidae mollusc lives a very different life style. From a Darwinian viewpoint, why do you think the shells of the Turbinellidae are so similar to shells of the Terebridae —an otherwise very different family of molluscs?
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Optional further items
15. Now return to the Five Principal Classes Page, and 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)
16. Comparing organ systems for gastropods versus bivalves, what uniquely different mechanism does the typical bivalve depend on for feeding? Among the bivalves, are there any exceptions to this feeding mechanism ?
17. Return to the Bivalve Family Index page, and examine information for both the Cardiidae (cockle) and Pectinidae (scallop) families. What do you think are the main differences in habitat for these two families? Why do you think the cockle shells are so ponderous compared to the delicate scallop shells?
18. Would you consider bivalves, in general, to be more or less primitive (ancestrally) compared to the gastropoda class? Why?
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