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Seashell Discovery: A Lesson in Inductive Classification Grades 4 to 8 Objectives: 1.To strengthen observation and communication skills 2.To build classification skills, and introduce students to scientific classification. Materials: 1. Kits of 10 to 15 shells per group of students. 2. Golden Guide to Seashells, (5.95 ea), one copy per group. Preparation and procedure Make up a kit of shells for each group of students. Try to get at least ten different types of shells in each kit. Place the shells in ziplock bags. Make sure each kit has the same number of shells, so you can hold kids accountable for returning the kits complete. Write the number of shells on the bag. Have the students count and confirm the number of shells when they beging, and again when they finish. Have some extra shells set aside so you can immediately replace any that turn up missing. This will help preserve your kits. Instruct students to examine the shells, observing texture, shape, pattern and structure. They should come up with any system of grouping the shells they like, and classify the shells. After they have them classified, they should give a name to each category, and write down a description of the features of each category. Make each student in the group take notes, so all are on task. Discuss with the entire class the categories which emerged, asking students to and describe their categories. Many groups are likely to have similar categories, perhaps with different names. Explain that people have observed these categories for a long time, and scientists have tried to agree on a common system of classification, so they can use the same terms to describe the same animals. Point out two basic categories of shells; the univalves, with one shell; and bivalves, with two shells. Hand out copies of Golden Guide to Shells, and have students turn to the overview of univalves, on page 4 and 5, which contains most of the groups they are likely to find. Ask them to see if they find any matches or overlaps with the categories they created. Ask them to add, whenever possible, the scientific name for the category to their notes. Their original classification system is legitimate, but they should understand the value of everyone agreeing on a common system. Point out that scientists try to base their categories on how closely organisms are related to each other. This corresponds closely to structural similarities between animals. Explain that basic structures are much slower to change than superficial features such as texture and color, and therefore provide a more accurate guide to actual relationships. You may also discuss why a variety of unrelated organisms may have evolved similar features, for purposes of camouflage, for example. Seashells and Scientific Classification After students have learned the scientific names of some categories of shells, you may wish to introduce the overarching system of scientific classification. This system creates a structure which divides living things into kingdoms, phyla, classes, orders, families, Genuses and species. The scientific name of any organism is the Genus (always capitalized, followed by the species; Homo sapiens, for example. Shells are, of course, of the animal kingdom, and of the phylum mollusca; the mollusks. Mollusks are then divided into several classes, the two largest of which are snails (aka gastropods, or univalves) and bivalves, such as clams and oysters. Other classes include cephalopods (octopus, nautilus and squid), tusk shells and chitons. Univalves are divided into three major orders, which are indicated on pages 4 and 5 of the Golden Guide. Easier to understand for children are the families. Most of the shells in your kits are likely to be common, and students should be able to find their families with some hunting. Shells within families have obvious structural similarities. Within a family, students will find shells grouped by Genus. The genus is often abbreviated after its first appearance to only one letter. Genuses are divided into species. A species is defined as a group of organisms which actively reproduce with each other. Extensions The inquiry approach to science education suggests that students be given rich resources to explore, and instruction consists of collaborative investigation of those materials. Extensions in line with this approach include brainstorming about reasons why shells might have developed certain structures, and where they might live. Further research in more advanced guides will reveal a great diversity of lifestyles of mollusks. Some are grazers of algae, while others, such as the cone shells, are active predators with venomous darts which can actually injure divers. Some, such as the shell-less nudibranch (pronounced nudibrank), use warning coloration to advertise their poisonous stingers. Some shells may show signs of predation, such as holes in the shell. What might have made those holes? How could it have done so? As students ask and are able to answer these questions, their confidence in themselves as researchers and problem solvers grows. The above ideas suggest considering the shells as organisms in the context of their habitat, including relationships with other organisms. Students may only be familiar with the shells as shells. Some guidebooks have beautiful pictures of the mollusks in their natural environment, revealing the soft structures we are not used to seeing. Some videos, such as Oceans Alive on PBS ITV, and Nature, Seasons in the Sea, show mollusks vividly. Nina Visconti-Phillips writes to suggest: Assessment alternative: Give them a shell they do not have already to classify Before Golden Guide use to assess understanding and ability to classify OR After Golden Guide use if you need to assess their knowledge and understanding of anatomy and classification within phylum mollusca. Bioethics One reservation I have about this lesson is that the careless harvesting of seashells for human use is endangering some species of mollusk. I feel that the use of common shells can be justified for educational purposes, and I believe most of the shells which are sold cheaply are picked up from beaches. I would suggest discussing this with students, however, and pointing out that some mollusks could be wiped out if people overharvest them. Resources Shells: The Shell Cellar on Pier 39 in San Francisco is my preferred source. They have baskets of shells for about $10. Three baskets should be sufficient for a class of 32. If you are lucky enough to be teaching in Oakland, you can borrow a kit I assembled from the BASTEC Resource Center. It is known as the Cody Seashell kit. It has shells and Golden Guidebooks. Books: 1.The Golden Guide to Seashells, ISBN # 0-307-24410-5, Golden Press, New York, 1985. 2.Eyewitness Handbooks, Shells; ISBN # 1-56458-060-1, Dorling Kindersley, New York,1992. 3.Encyclopedia of Marine Animals; ISBN # 0-207-16429-0, Angus Robertson (Harper Collins), New York, 1991. This book is a good source of photos of living mollusks. Mollusk Internet Links: Smithsonian Bibliography of Mollusks