Lesson Plan 1- Meeting an Earthworm

Students participating in the National Worm Survey must use the Key to Reproductively Mature Earthworms Found in Canada. Before they can use this key, students must become familiar with the anatomical features of an earthworm. This activity is designed to introduce students to earthworms and their anatomy. It is also intended to encourage students to practice their science skills of observation and recording information.

Students will develop an understanding of the nature of science as well as the social and environmental contexts of science and technology.

Students will develop the skills required for scientific inquiry, problem solving, communicating scientific ideas and results, working collaboratively, and making informed decisions.

Students will construct knowledge and understanding of concepts in life science and apply these understandings to interpret, integrate, and extend their knowledge.

Students will be encouraged to develop attitudes that support the responsible acquisition and application of scientific knowledge to the mutual benefit of self, society, and the environment.

Key Terms: prostomium, peristomium, body segment, genital tumescences (GT), clitellum, tubercula pubertatis (TP), setae, periproct, anterior, posterior, dorsal, and ventral

Figure 1. The anatomy of an earthworm

Additional Science Information

Invertebrates Earthworms are invertebrates. That is, they do not have a backbone. Insects, sea stars, spiders, jellyfish, and millipedes are other examples of invertebrate animals. Segments Study the illustration of an earthworm shown below. You will notice that earthworms have long, cylindrical body that is divided into similar segments. The grooves that extend around the body of the worm show the arrangement of the segments. Some species of earthworms have a body composed of over 100 segments. How many segments does your earthworm have? Symmetry Earthworms have bilateral symmetry. This means that if you cut the earthworm down the centerline, the left side of the body would be identical to the right side. Body Colours One of the key features of an earthworm is the colour of its body. Some species of earthworms have a dark-red or red-violet body while other species are muddy-green. However, there are species that do not have these colours. For the purposes of Worm Watch, these animals are said to have "other body colours." Prostomium Some species of earthworms have a tongue-like lobe above the mouth called prostomium. The prostomium is actually a sensory device. Earthworms do not have a nose, eyes, ears, or hands to gather sensory information about their environment. Instead, they depend on their prostomium and sensory receptors in their skin to "feel" their way through the soil. Peristomium The first body segment is called the peristomium. The peristomium contains the mouth. Clitellum Adult (sexually mature) earthworms have a distinct swelling called a clitellum. It is located about one-third of the way down the earthworm. The clitellum is often white or orange in colour. It produces most of the material secreted to form earthworm cocoons. The clitellum forms a band that can be flared, non-flared, saddle-shaped, or annular. It is generally found between segments 26 and 33. The clitellum is only found on adult worms. Young or juvenile worms do not have a clitellum. The clitellum of each species of earthworm has a distinct colour, size, and shape. Another key structure found on the clitellum is the tubercula pubertatis. The diagram shows the shape and structure of the clitellum. They may have any combination of shapes. Tubercula Pubertatis (TP) The tubercula pubertatis (TP) is another structure used to identify earthworms. The TP are glandular swellings located on both sides of the clitellum. They can assume a variety of shapes such as long and narrow, triangular, or sucker-like. The shape and location of the tubercula pubertatis (TP) on the clitellum are key features used to identify mature earthworms.] Genital Tumescences (GT) The genital tumescences (GT) are areas of modified epidermis (skin) that do not have distinct boundaries. These are openings through which follicles of genital setae open. The pattern and location of the GT are important clues to identifying different species of earthworms.] Anterior Locate the clitellum of a mature earthworm. The shorter region to one side of the clitellum is the anterior or head-end of the animal. This end of the worm is usually more pointed than the posterior end of the animal. The prostomium is the first segment at the anterior end of the animal. Posterior Locate the clitellum of a mature earthworm. The longer region is the posterior or tail end of the earthworm. Dorsal The top-side of an animal is called the dorsal surface. For example, the fin you see in all shark movies shows the dorsal fin of a shark just before it attacks. The dorsal surface of some species of earthworms is darker than its ventral surface. Ventral The bottom-side of an animal is called the ventral surface. In many animals, the ventral surface is a lighter colour or shade than the dorsal surface. Periproct The periproct is the last segment of an earthworm. Setae Each segment, except the first and last, have tiny bristle-like structures called setae. These structures help the earthworm to move and act to sense the environment. The number and arrangement of setae are important clues to the identification of earthworms.] Epidermis The epidermis is the name for the skin of an earthworm. It is the outer layer of worm and it secretes a mucous.

Activity Preparation

Suggestion: Ask the students to bring worms from their garden or somewhere near their home where they have permission to sample. Then the students can practice sorting the earthworms into adults and juveniles. It is important to have adult earthworms for this activity so the students should try and bring a good selection of earthworms but at the same time try to minimise damage to the garden.

For the Investigation

Implementation Strategies

Go over the instructions with your students. You may have to read the instructions to younger students. Make sure they understand that earthworms should be handled carefully and treated with respect.

If you do not have access to a computer during this investigation, you may want to download the Earthworm Anatomy notes found in the Worm Watch Resource section of the web site. Photocopy and distribute one set of notes for each team.

Ask your students to copy the data charts into their science notebook before giving them the earthworms.

Students should collect all of the materials before they are given the earthworm. Remind the students to keep their earthworms covered with moist paper towels throughout this investigation.

In the first part of the investigation, students make observations and record these in a data table. Encourage students to make very detailed observations and to use their sense of touch as well as sight.

In the second part of the activity, students look at the anatomical features that they need to find in order to identify the earthworm. Students do not need to memorize the names of these structures. However, they do need to be able to find these structures and recognize the patterns made by the GT and TP within the area of the clitellum. The patterns of the GT and TP are unique to each species of earthworm.

Hints and Suggestions

Make an overhead transparency or use an computer-projection system to show the genital tumescence (GT) and the tubercula pubertatis (TP). Students may be concerned with the long names but these are very important features used to identify worms.

Once again, earthworms do not like the light. Students should keep the worms covered with a moist paper towel as much as possible throughout the activity.

Caution students about a hand lens and the damage it can cause to their eyes as well as to the earthworm. Some students may have started a fire with a hand lens - you MAY want to use this as way to remind them about the dangers of looking at the Sun.

Caution students to wash their hands with soap and water when they are finished this investigation.

Place unwanted worms into a bag and put them into the freezer overnight. The worms can then be used for compost or fish food.

Wrap-Up

Have students return their earthworms to the container and clean up the mess.

Use an over-head transparency or other means to review all of the main features of the earthworm with your students. Or, photocopy an illustration of an earthworm and have students label all of the key structures.

Extensions

1. Earthworms belong to the Phylum Annelida. Use your library and/or the Internet to locate information on other worms found in this phylum.
2. There are other activities relating to soil ecology in Discover Soil.

ICT Integration

1. Design and develop a multimedia presentation that describes the external features of an earthworm.
2. Design and develop a web page that describes the external features of an earthworm.
3. Design and develop a database that includes all of the external features you have studied to this point.
4. Use graphics software to create an earthworm poster.

Cross-Curricular Connections

1. Make a model of an earthworm out of modeling clay or play-dough. Encourage students to place all of the structures they observed in the investigation on their model.
2. Write a poem or story about the earthworm they have observed.
3. Draw a poster that shows the anatomy of an earthworm.

Assessing Student Learning

Rubrics are rating scales commonly used to evaluate student performance. These scoring guides can be used to evaluate a wide variety of activities. They are quick and efficient methods of subjectively evaluating progress. However, you can make this form of evaluation more objective by making the criteria more specific. The more specific the criteria, the more feedback you will providing your students. The following is a sample rubric that you can use to evaluate the students in this activity.

Performance Indicators

Black Line Masters

• Blank Worm Diagram [48k PDF] - Use the Key Terms in this lesson to label the parts of the earthworm.