Topic: Annelids

Author: Elżbieta Szedzianis

Target group

6th grade students of an eight‑year elementary school.

Core curriculum

5. Annelids. Student:

a) presents the living environment, the morphological and the adaptive features of annelids to their lifestyle,

b) observes the representatives of annelids (photos, films, drawings) and presents their common features,

c) presents the significance of annelids in nature and for the humans.

Lesson aim

Students describe the build, lifestyle, adaptive features and biological significance of the annelids.

Key Success Criteria

• you will observe an earthworm, describe its body and give 3 examples of how it adapted to the life on land and 2 examples of its adaptive features to live in the ground;

• you will recognize a leech and distinguish annelids from other animals;

• you will give example that earthworms are necessary for the ground.

Key competences

• communicating in a foreign language;

• Mathematical competence and basic competences in science and technology; 

• learning to learn;

Methods/forms of work:

A talk, work with text, workshop method.

Individual or group work.

Teaching measures:

• abstract;

• interactive whiteboard or traditional blackboard;

• tablets/computers;

• worksheets;

• examples of earthworms;

• coarse paper;

• magnifying glasses;

Lesson plan overview (Process)

Introduction

1. The teacher asks the students, if they ever wondered where the Polish name for earthworm (dżdżownica) comes from. He explains the word comes from an Old Slavonic word deżdż, meaning rain. It was noted that earthworms leave their holes in the ground to the surface after heavy rain. He asks the students to propose an alternative modern name for these animals. The students then select the best suggestion (it has to be connected with the behaviour and the built of an earthworm). Then, the teacher informs students that during today’s lesson they can use a traditional or new name for this animal.

2. The teacher explains what today’s lesson is about and what the criteria of success are.

Realization

1. The teacher asks the students to read the following texts and do the following tasks:
a. title texts A through C,
b. decide, which facts they can confirm through observation, and which through experiment,
c. plan observations and experiments.

Text to be read by the students (included in the worksheet):
A. Earthworm holes allow the access of air and water into the ground.
Earthworms mix the ground.
Earthworms excrete digested rests of organisms. Their excretion consists of substances that are needed for plant growth.
Earthworms are the food of many animals.

B. Earthworms prefer moist rather than dry soil.
They take in air necessary for breathing with the entire surface of their moist body through an outer moist body layer.
Sometimes, earthworms come out to the surface at night, if the air is moist.
Sometimes, earthworms carve their holes deep in the ground in order to avoid draught or freezing.
Their worm‑like shape of their body allows them to carve their holes and move in them easily.

C. The body of an earthworm consists of many segments - called metamerisms.
Every segment has bristle‑like hairs called lateral setae, which allow earthworms to move. You can feel them when you touch the belly of an earthworm with your finger running from the back to the front.
Earthworms do not have a typical spine, but they have many muscles. At the front of their bodies, earthworms have mouths, and at the end they have anus.
They do not have eyes.
The outer part of their body is sensitive to touch, light and chemical substances.
Earthworms have red blood, which can be seen through their body.

2. Students discuss the exercises. The teacher writes down the best ideas for observations and experiments, which cannot be carried out during this lesson plus includes the names of their authors. He will then propose the authors participate in research projects after class and will invite them to extracurricular classes.

3. Students split into groups and they start the observation of the external built and the movements of an earthworm. The animals are put on a coarse sheet of paper in order for the students to be able to hear the movement of the lateral setae on the surface. The students observe the animals. Facts about earthworms written down in the worksheet which can be confirmed during this observation should be underlined and, if necessary, other information should be added.

4. Teacher explains that leeches are close cousins of earthworms. He asks the students to watch the movie from the Internet titled „Shape of Life: Annelids - Leeches” and comment what they see (the build of a leech, how it moves, how it feeds, and why does it belong to annelids).

Summary

1. The teacher asks the students to talk about how earthworms and leeches are adapting to
   ● living on land,
   ● living in the ground,
   ● moving around
   ● parasitic lifestyle.

2. Students finish the sentences:
   During this class I liked …
   During this class it was difficult to…

Optional homework

Complete interactive task 1.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Annelids

Annelids live mainly in fresh and salt water but terrestrial species are also known. Most of them lead an active lifestyle – they dig underground corridors, crawl on the bottom of water reservoirs or dig them, float under the surface of water. Some species are sedentary. The rear end of the body is attached to stones located on the bottom. They can also settle on the armour of other organisms. Their bodies are often hidden in special tubes that are also called houses. These tubes are made of mucus secreted by the annelid's body and materials available in the animal's surroundings, such as sludge and sand grains. Species that lead an active lifestyle have two‑sided symmetry, and those leading a sedentary lifestyle usually have radial symmetry.

Annelids have vermiform bodies divided into segments also known as rings. They do not have a hard skeleton. It is replaced by fluid that fills empty spaces inside the body with no organs. Under the epithelium covering the body there is a thick layer of muscles that allows changing the shape of the body and moving around.

Earthworms, which lead an underground lifestyle, feed on dead organic matter found in the soil. They eat huge amounts of soil, and acids contained therein are neutralized with special limestone glands escaping into the oesophagus. They digest organic substances found in the substrate, and excrete mineral components from the body in a form easy to assimilate for plants.

Leeches are mostly external parasites. They feed on the blood of their hosts. They have suction cups on the front and back of their bodies. They use them to attach to the host and cut its skin with teeth in the mouth hole placed inside one of the suction cups. Leeches put in an anaesthetic substance into the victim's body thanks to which the victim does not notice the presence of the parasite, and hirudin, a substance that prevents blood from clotting. Leeches suck a large amount of blood at one time, and then they store it in the crop, a part of the digestive tract. Digestion can last up to 2 years. Some leeches and some marine annelids are predators. They hunt their prey, mainly small crustaceans and mollusks, chasing them in water.

Earthworms and leeches are both hermaphrodites. They are characterized by simple development, i.e. without the larva stage. There occurs cross fertilization, during which two annelids stick together with the abdominal sides of the body and exchange sperm. They release large amounts of mucus used to connect them and to which gametes go. It transforms into a cocoon in which fertilized eggs will develop. The number of eggs therein is from 1 up to 300. Cocoons are deposited in the soil, on plants, stones or on the abdominal side of the parent organism.

Annelids, mainly earthworms, participate in soil formation and fertilization, and improve its structure. Their underground corridors scarify it, thanks to which other soil organisms and plant roots have better access to oxygen, and the loose substrate absorbs and retains large amounts of water. Earthworms eat leaves and manure particles, accelerating the decomposition of organic matter. Their impact on soil quality is so great that they are deliberately bred and then used to decompose waste from slaughterhouses or fruit and vegetable, paper, sawdust, sewage sludge processing plants. They transform it into a very valuable fertilizer that is called biohumus.

Marine annelids, which live at the bottom and feed on dead organic matter, contribute to purification of water.

Annelids are a valuable source of food for many groups of animals, such as cancers, insects, fish, amphibians, birds and mammals. They are often used as a fishing bait or food for aquarium fish. Some predatory leeches and marine annelids balance the numbers of other organisms, mainly small crustaceans and molluscs. Leeches parasitizing fish cause considerable damage in their breeding. The ability of leeches to suck blood is used in the treatment of many diseases, such as: hypertension, ischemic heart disease, varicose veins and limb oedema. Applied to wounds after surgery, skin transplants and burns, they accelerate healing.

• Annelids are animals with worm‑shaped bodies composed of segments (annuli).

• Annelids are: saprophages (earthworms), parasites (most leeches) or predators.

• Annelids that live underground do not have legs or eyes.

• Annelids contribute to soil fertilization and purification of water reservoirs.