Structures of Life
Plant and Animal Care

Students investigate the following animals in the Structures of Life Module

Crayfish
Elodea
Land snails

Click on any animal to find out specific information about its care.

Introduction to Life in the Classroom

In several of the FOSS modules and courses, living organisms are brought into the classroom to be cared for and observed by K-5 students. Through the direct experience with organisms provided by these modules, we hope to engender in students a sense of respect for all life and to spark a desire to understand the complex systems that support life on Earth.

The FOSS program endorses the National Science Teachers Association Guidelines for Responsible Use of Animals in the Classroom as they apply to elementary and middle school classrooms.

The FOSS program provides detailed information on how to obtain organisms, how to prepare for their arrival, how to care for them in the classroom, and how to instruct students to properly handle each animal. The animals in the modules were selected because they are abundant, safe for students, easy to care for, and hardy and well-adapted to classroom environments. FOSS selected organisms that were nonexotic, commonly available from local and regional suppliers, and, in some cases, found in the natural environments in many regions. When investigations are carried out as described in the FOSS teacher guide, the insects, worms, crustaceans, snails, and fish are not harmed in any way.

To read more about the FOSS/Delta Policy Statement on Living Organisms in the Classroom, please click here.

CRAYFISH



Crayfish are marvelous classroom organisms. They are exciting and easy to care for. Through close observation, students can learn interesting details about animal structures while developing sensitivity to the needs of living organisms. Crayfish can act like living magnets, keeping students in at recess and drawing students into your classroom from all over school. In short, crayfish can bring new life to your classroom.

Crayfish are crustaceans. Their appearance is bizarre—they are festooned with a bewildering array of walking legs, pincers, and other appendages for eating, feeling, and attending to other crayfish business. Equipped with thousands of sensory bristles, some sensitive to chemicals and the others to touch, crayfish can smell, feel, and hear acutely, even though they are completely covered in a hard shell. They are aquatic, but can survive fairly extended sojourns on dry land as long as their gills remain moist. In order to meet the crayfish up close and personal, let's review some of this animal's natural history.

Crayfish like it dark and cool, and during much of the daylight they will be found alone, withdrawn under a rock or a clump of vegetation, waiting for dark, at which time they come out to forage for food. Crayfish are omnivorous, eating just about anything they can find or catch, dead or alive. Large food is held and torn to pieces in the large pincers and conveyed to the mouth by the smaller specialized legs near the head. That's what crayfish mostly do: loaf all day and look for food all night.

Crayfish are terrific animals for your students to study. They walk, swim, eat, hide, breathe, mate, molt, and die right in the classroom. Your crayfish container is a microcosm of life on Earth, and students will learn a lot by sharing time with crayfish.

Reproduction. But there are times in a crayfish's life when the routine is broken. Males and females, spurred on by messages communicated to each other, join periodically for mating, especially in the spring. Males can be told from females by the generally larger pincers and narrower tails, but these characteristics are not absolute. To tell for sure, you must pick them up and look underneath. Males have two pairs of modified swimmerets (the small leglike appendages under the tail) that are white-tipped and lay between the last pair of walking legs. The females have longer, softer-looking swimmerets (for holding the eggs) and a little white pore centered between the walking legs. Some time after mating the female lays about 200 eggs, which she carries in a mass under her tail.

After several weeks the eggs hatch, and a hoard of minute, perfectly formed, ravenous baby crayfish emerge. At first they continue to ride along under the female's tail, eating tiny waterborne bits of food, but soon they leave this security and head out on their own. During these early days many are eaten by fish, insects, and other crayfish, but some always survive to fulfill their destiny.

Pregnant crayfish. You think you might have a pregnant crayfish? Here are some things to consider.

Molting. Another ponderable: think about the problem of living inside a suit of armor. Crayfish can't grow unless the shell (comprising the carapace, or main body shell, tail shell, and leg shells) can be removed. And this is exactly what crayfish do. Periodically (quite often early in life) the crayfish slides out of its old, hard shell in a process called molting. The "naked" crayfish that emerges is actually covered in a complete and perfect shell, but it is soft and flexible, allowing the crayfish to expand and grow. After a day or so the new shell will become hard, again affording the animal the protection of an armored exterior.

In preparation for molting the crayfish withdraws most of the calcium from its shell, and stores it in two white "tablets"in the sides of its head. Calcium is a major hardener in the crayfish shell, as it is in strong human bones and teeth. With this precious supply of calcium the new shell can harden in a matter of hours instead of days or weeks.

Ordering crayfish. There are a number of ways to get crayfish for this activity. Have students catch crayfish from a local creek or pond; buy them from a bait shop; or order them from a biological supply company. In any case, you will need 10–12 healthy crayfish that are accustomed to still, relatively warm water (as opposed to cold, fast-running streams).

If you purchase the crayfish from a biological supply company, place your order for one dozen medium-size crayfish well before the investigation. Let the company know on what date you plan to introduce the crayfish to your class. Use a local vendor if possible.

Preparing for crayfish arrival. A day or two before you expect the crayfish to arrive, prepare their habitat. Fill two bus trays about one-third full of cold tap water (3–4 cm deep). Keep the trays out of sight in a cool, dark place. Let the water sit for a day or more to release chlorine from the water.

What to do when they arrive. The crayfish will arrive in a cardboard box packed with damp paper or moss. Alert the school secretary to notify you as soon as they come. Immediately upon arrival, cut open plastic bag to provide air. Keeping bag upright, float entire contents in prepared bus tray for 15 to 30 minutes to equalize water temperatures. Carefully remove crayfish from the bag, grasping each from behind to avoid the strong pincers. Aquatic plants shipped with the crayfish can be rinsed in clean dechlorinated or spring water and used as both food and "hiding" places for the crayfish. Maintain at cool room temperatures, out of direct sunlight.

Handling the crayfish. Practice picking up the crayfish so that you can demonstrate the proper technique for your students. Approach the crayfish from behind. Grasp it firmly on the carapace (body shell) behind the pincers. Pick it up. It may try to reach back, but don't worry—it will not be able to reach you.

Provide aquatic plants. Buy or collect from a local pond some small aquatic plants for the crayfish. We recommend getting 6–12 sprigs of Elodea, also known as Anacharis. (It looks like a little green feather boa.) You can order it from a biological supply company when you order your crayfish, or you can pick it up locally at a pet store that deals with fish. If Elodea is not available, try another inexpensive aquatic plant.

Find a place for the crayfish. Plan where the two bus trays with the crayfish will reside in your room for up to several months. They need to be cool, out of direct sunlight, and safe from being spilled.

Prepare for care and feeding. Crayfish need ample clean, cool water and sufficient food in order to be healthy in your classroom. It is virtually impossible to get the water too cold (short of freezing), but it is easy for it to get too warm. Try to keep the temperature between 5°C (41°F) and 20°C (68°F).

You will feed your crayfish protein in the form of dry cat food that sinks in water. Don't worry if the crayfish don't eat for a week or two; they will eat when hungry. Always move the crayfish out of their home tray and into a basin with 3–4 cm of water to feed them the dry cat food. Put in one piece of cat food per crayfish. Leave them there for about 1/2 hour. (If they don't eat, they aren't hungry.) Then return them to their home tray, without any of the cat food. The other food source that is always available is the Elodea that stays with the crayfish in their home trays.

This feeding routine can be followed every day if the crayfish are actively eating, and less frequently if they are not. While they are in the feeding basin, the home tray can be rinsed and filled with fresh water. This should be done about once a week—more often if the water begins to smell bad.

Plan for a new crayfish home. When you have completed the activities, there are several options for disposing of the crayfish. Discuss the options with students and together come up with a plan.

Resolving the question of what to do with the crayfish can be turned over to students. They can do research by writing or calling local experts to find out what they recommend. One expert to talk to might be the company that supplied the crayfish. Local fish and game biologists would be another resource for students to contact.

Crayfish pose no health hazard for students. They do not carry diseases. Occasionally you will see white wormlike animals attached to the crayfish carapaces and pincers. They are harmless to both humans and crayfish. They seem to be opportunists, riding along for a free meal when the crayfish eat. 

Oregon Public Broadcasting video on invasive crayfish.

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ELODEA (ANACHARIS)


Plants occupy the base of the food pyramid in aquatic systems just as they do in terrestrial systems. Inconspicuous single-celled algae that turn your aquarium green capture the sun's energy and provide food for countless minute animals in the water. If you want to stimulate an algae bloom (population explosion), put a goldfish in an aquarium, place it where it will get direct sun several hours a day, and provide the fish with plenty of food. When you see the water turn green, it's a sign that your aquatic plants are growing beautifully.

FOSS activities also use vascular aquatic plants. The popular goldfish-bowl plant that looks like a green feather boa is Elodea (or sometimes Anacharis). In nature it is usually rooted to the bottom of a stream or pond, but in your aquarium it can just float around. It is a good food source for amphipods, fish, and crayfish and will contribute to the oxygen in the water as it photosynthesizes. It also provides crannies where small animals can hide from predators.

Care of aquatic plants is easy. Keep plenty of water in their container.

What to do when the plants arrive. Open bag and rinse plants in dechlorinated or spring water. Keep Elodea floating in bowl of dechlorinated or spring water to avoid drying out until it's ready to use.

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LAND SNAILS


The land snail is one of nature’s marvels. But many of its finer attributes go unrecognized because of its reputation as a garden raider. Because it takes a toll on our spinach, cabbage, and lettuce as it goes about its business of survival, we find ourselves in a conflict relationship. In the classroom, however, traditional animosities are put aside in the interest of learning more about the diversity of life.

Land snails are gastropods, whose members also include aquatic snails (including marine snails) and slugs. The name means stomach-foot. This makes a degree of sense as the whole clan gets about by gliding on a muscular structure on the bottom of the abdomen, called the foot. The action that produces motion is a well-coordinated, wavelike contraction of muscles on the bottom of the foot that propels the gastropod smoothly forward over just about any surface. The action is not fast by human mobility standards, but you and your students will be amazed by how far snails can travel when your back is turned for what you think is just a moment. A determined snail can easily cover a meter in 5 minutes, so in the course of an evening a snail can travel the length of a football field and back. If the lid came off your terrarium in the evening, you can figure out how far and wide those snails might range in your classroom.

Land snails have several characteristics that make them easily identifiable. They have a single shell, usually coiled, that is a combination shield and humidor. The hard shell resists the efforts of predators and provides a haven during dry times. Snails are a moist gang, and if a snail cannot find a watering hole to renew its water supply, it will retreat to a protected nook, withdraw into its shell, and seal its shell to a solid surface. The snail will lapse into dormancy until rain, dew, or a garden sprinkler once again moistens the environment. This passive state, rather like hibernation but initiated by dry rather than cold, is called estivation.

One indication that snails have been active is the telltale slime trail. Garden snails produce a layer of mucus on which they slide. This makes it easy to track their movement, but also saddles them with a reputation for being yucky. Students may find this fact a bit repulsive at first, but will quickly forget it when they become absorbed in observations of these fascinating creatures.

Most land snails have interesting projections on the fronts of their heads. Students will identify them as feelers or antennae. They will see two long ones on top of the head reaching up, and two smaller ones reaching down. Technically they are tentacles, but “feeler” is a pretty good description of their function because they are touch sensitive. The two longer ones have light-sensitive organs at their tips, making them the snail’s version of eyes, although their function is limited to light perception rather than image generation. The shorter tentacles feel, taste, and smell the environment in the never-ending search for food and water, and in constant vigilance against dangers.

The snail’s mouth is on the bottom of the head right up by the short tentacles. Inside the mouth is a specialized eating tool, the radula. The radula is a muscular structure covered by thousands of tiny, sharp teeth. The snail eats by pressing the radula against a leaf or other desirable bit of vegetation and rasping it to scrape away small particles. This action can be seen if students feed a hungry snail some lettuce or apple.

Most other interesting snail structures are hidden inside the shell, but some can be observed with patience and perhaps a flashlight. Snails breathe by taking air into a visceral cavity that is richly supplied with blood vessels—the snail’s version of a lung. When the snail extends from the shell, the access pore can be seen opening and closing just below the margin of the shell on one side. Also, the snail’s heart can be seen pumping blood by placing a snail on the lens of a flashlight and carefully looking through the translucent shell.

The shell itself is an excellent piece of work. The colors and patterns are lovely, and the coil is a masterpiece of efficient construction. Snails grow by laying down new material around the edge of the roughly circular opening. By extending the length and diameter of the living quarters, the snail can grow and still retreat into its shell as needed. The shell is rich in calcium, so snails need a continual supply in their diet. In the classroom calcium is available from plain chalk or a piece of cuttlebone in the snail terrarium.

Most land snails are hermaphroditic, holding under one shell both male and female reproductive potential. However, snails must mate in order to fertilize each other’s eggs. Eggs, the size of BBs, deposited in soil, will hatch in a few weeks into perfectly formed little snails, fully mobile, ready to ravage your garden.

What to do when they arrive. The largest and friendliest land snail for the classroom is the escargot snail that is naturalized in California, Helix aspersa. If you live in a region where Helix has become established in local gardens, collect them locally. If you cannot collect them locally, order them from Delta Education. Land snails are quite hardy and can survive for many days with little food or water. In your classroom, they will live in two clear terrariums with covers (the same type of basins as used for the hydroponic plants). Once the snails arrive, place moist paper towels on the floor of each terrarium and spray the interior walls with water. Distribute the snails into the terrariums and provide a few small pieces of carrot or other vegetable for them to eat. Snails are strong! Secure the cover with two large rubber bands stretched around the terrariums.

Maintenance. In a natural habitat, land snails eat leaves, mushrooms, fruit, and many other kinds of plant material they find. In the classroom, they must be fed and their habitat must be cleaned. Here's the weekly care and feeding routine.

The question of what to do with the snails when the investigations are complete is a sensitive one and in part is determined by where and how you obtained the land snails. Potentially, the best solution is to keep them in the classroom and institutionalize their care, continually creating an ever more complex and interesting environment for them to live in. Continue informal investigations, particularly watching for life cycle. If you obtained the land snails from a supplier out of state with a USDA permit process, you must comply with the federal regulations on what to do with the snails. For snails that are not collected locally, release into the environment is never an option. If no other option is possible, the most humane thing to do is euthanize the snails by collecting them in a bag and placing them in the freezer. Then dispose of them in the trash.

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