Biology and Health Sciences

Activity 1. 9: To examine features
of animals in phylum Arthropoda
You will be provided with pictures
or photographs of animals in
phylum Arthropoda.
1. Observe the external features of
the animals.
2. Discuss with your class members
the features observed.
3. Write down the common features
possessed by the different groups
of organisms.
4. Note the number of body parts,
legs, antennae and eyes.
5. Summarise the features of the
different groups of organisms in
a table.What are arthropods? How do they differ from chordates?
Look at the pictures in fig 1.10. Can you identify the animals in the pictures? Come up with a list of the differences between these animals and chordates.

The word arthropod comes from two words ‘Arthros’ meaning ‘jointed’ and‘poda’ meaning ‘leg’ or  ‘foot’. Therefore arthropods are animals with jointed appendages. It is the largest phylum in the animal kingdom. The animals in this group inhabit land, water and soil. Some arthropods are useful in many ways, for example:
• Butterflies and bees act as pollinators of flowering plants.
• Bees make honey.
• Lobsters are used as food. Some arthropods are harmful to other living organisms, for instance:
• Ticks transmit diseases in animals.
• Mosquitos transmit malaria.
• Tsetse flies transmit trypanosomiasis.
• Aphids destroy crops such as maize, coffee and cassava.

Main characteristics of organisms in phylum Arthropoda

Activity 1. 9: To examine features of animals in phylum Arthropoda You will be provided with pictures
or photographs of animals in phylum Arthropoda.
1. Observe the external features of the animals.
2. Discuss with your class members the features observed.
3. Write down the common features possessed by the different groups of organisms.
4. Note the number of body parts, legs, antennae and eyes.
5. Summarise the features of the different groups of organisms in a table.

I have discovered that… Organisms in phylum Arthropoda can further be grouped into various classes.
The organisms are grouped on the basis of:
• Number of legs
• Presence and absence of antennae
• Number of antennae
• Number of body parts
• Type of eyes

The 5 classes of phylum Arthropoda are:
a. Insecta
b. Arachnida
c. Crustacea
d. Diplopoda
e. Chilopoda

Class Insecta

This is the largest class in the phylumn Arthropoda. The term ‘insecta’ comes from the word ‘incised’ which means ‘cut.’ The body of organisms in this class are divided into three distinct parts; that
is head, thorax and abdomen. look at the pictures below. Can you identify the different insects?

Activity 1.10: To observe the external features of insects
Requirements
• Sweep nets
• Hand lenses
• Glass jars
• Gloves
Procedure
1. Collect a large variety of insects from the school compound.
Caution: Avoid catching dangerous insects like wasps and bees as they can sting you.
2. Use sweep nets to catch flying or jumping insects like houseflies and grasshoppers.
3. Put them in glass jars and take them back to the laboratory for observation.
Note: To make observation easier, some insects can be immobilised using chloroform.
 Precaution: Do not inhale chloroform. It is toxic.
4. Examine the specimen carefully and note the following features.
(a) The number of body parts.
(b) The types of eyes: simple or compound.
(c) Presence or absence of antennae.
(d) Presence or absence of wings
(e) Number of legs.
5. Draw and label clear diagrams of the specimen.

Study questions
(i) Insects have ……………..body parts?
(ii) Insects have…………….pairs of legs?
(iii) Draw well labelled parts of an insect.

My environment, my life!
Do not kill the insects. It is important to release insects after observation while they are still alive.

Main characteristics of organisms in class Insecta

1. They have three distinctive body parts; head, thorax and abdomen.
2. They have a pair of long antennae.
3. They have three pairs of jointed legs, which are attached to their thorax.
4. They have a pair of large compound eyes.
5. Some have one or two pairs of wings that are attached to the thorax.
6. They breathe by means of spiracles,which are found on the sides of the abdomen and thorax.

Class Arachnida

This class of arthropods includes spiders, mites, ticks and scorpions.

Activity 1.11: To examine the main features of class Arachnida
Requirements
• Hand lens
• Live or preserved specimen or photographs of any of the following organisms: spiders, ticks or mites.
• White tiles, papers or petri dishes Caution: Some animals in this class like spiders can be poisonous.
Procedure
1. Using a hand lens, examine the specimen provided.
2. Note the following
• Number of body parts.
• Number of legs.
• Presence or absence of antennae.
• Presence or absence of wings.
• Number and type of eyes.

Study Questions

1. How many body parts can be observed in the organisms?
2. How many legs do they have?
3. Do they have any antennae?
4. Describe the type and number of eyes present in the organisms.
5. Do the organisms have wings?

Main features of organisms in class Arachnida

1. The body is divided into two parts: cephalothorax and abdomen. The head and thorax are joined to form a cephalothorax.
2. They have four pairs of jointed legs attached to the cephalothorax.
3. They have simple eyes about 8 in number.
4. They do not have antennae. Instead they have a pair of pedipals.
 5. They posses a pair of poison glands called chelicerae.Class Crustacea Have you come across a crab, wood louse or water flea? All these are Crustaceans. Other animals in this class include lobsters, crayfish, shrimps and barnacles.

The term crustacea is derived from “crusta” which means a ‘hard shiny coat’. They are aquatic  arthropods except for wood lice which are the only fully terrestrial crustaceans.

Activity 1.12: Investigating external features of class Crustacea
Requirements
• Live specimen, preserved specimen or pi c tures or illustrations of crustaceans like crayfish, crabs, prawns, lobsters and shrimps.
• Hand lens
Procedure
1. Identify the specimens you have been given.
2. Examine the specimens and note the following for each specimen:
• Number of body parts.
• Number of antennae.
• Position of the eyes.
• Type of eyes.
• Types and number of appendages present.
• Nature of the carapace.

Study questions
(a) How many body parts are observed on each of the specimen given?
(b) Comment on the number and nature of antennae.
(c) How many walking legs can you observe on the specimen?
(d) Are the eyes on the specimens simple or compound?
(e) How many types and number of appendages are present on the organisms?
(f) What is the nature of the carapace?

Main characteristics of organisms in class Crustacea

1. Their body is divided into two parts: the cephalothorax and the abdomen. The head and the thorax are joined to form the cephalothorax. The cephalothorax is covered by a shiny coat known as carapace.
2. They have different types of appendages. Their appendages are modified to form legs for walking, feeding, protection, and for swimming.
3. They have two pairs of antennae.
4. They have a pair of compound eyes at the end of stalks.
5. They have ten or more legs. The walking legs are usually located on the cephalothorax while the
swimming legs are located in the abdomen.
6. They breathe by use of external gills on the underside of the carapace. Class Diplopoda Diplopoda means arthropods wi th two pairs of legs per segment. They also have elongated cylindrical bodies. Diplopods are herbivores and mainly feed onvegetables and dead organic matter. This class c onsists of millipedes. Millipedes are of various sizes. There are giant millipedes and small sized millipedes.

Activity 1. 13: Investigating the characteristics of class Diplopoda
Requirements
• Hand lenses
• White tile or a white piece of paper
• Petri dish
• Millipedes (live specimens, pictures, illustrations or preserved specimen)
Procedure
1. Place the specimen on the petri dish or white tile.
2. Examine the specimen carefully using a hand lens.
3. Observe the following features:
• The number of legs on the organism.
• Number of legs per segment, and position of legs on the segment.
• Number of body parts.
• Presence or absence of antennae.
• Number of antennae.
• Type of eyes.
Study questions
a) Millipedes have ……………..legs per segment?
b) What type of eyes does a millepede have?
c) Millipedes have …………body parts.

Main characteristics of organisms in class Diplopoda

1. They have elongated and cylindrical bodies.
2. Their bodies are divided into two main parts; the head and a segmented trunk. The number of body segments ranges from 25 – 100.
3. Each body segment has two pairs of legs except the first thoracic segments that have one pair of leg each.
4. They have a pair of antennae.
5. They may have simple or compound eyes, or in some cases no eyes are present.
6. They breathe through spiracles found on the sides of the body segments.
7. Millipedes roll their bodies when disturbed. After coiling, they produce a stinking substance from their  stink glands. This is self- protective behaviour against enemies and preators.

Class Chilopoda

This class is composed of centipedes. They are found in virtually all habitats but unlike the millipedes, they have less

number of legs. Centipedes have only one pair of legs per segment.
Activity 1.14: To investigate the characteristics of centipedes
Requirements
• Preser ved specimen of a centipede, illustration or picture of a centipede.
• White tile or paper
• Hand lens
Caution: Centipedes have poison claws and should never be handled when alive.
Procedure
1. Place the specimen on the white tile or white paper or petri dish (in the case of preserved specimen).
2. Examine the specimen carefully using a hand lens.
3. Note the following observable

features:
• The number of legs on the organism.
• The number of legs per segment and position of legs on segment.
• Presence or absence of wings.
• Number of body parts.
• Presence or absence of antennae.
• Number of antennae.
• Type of eyes.
 4. Study the first segment after the head.Note the large structure with a claw at its end, projecting from the first segment. It is called a poison claw.

Study questions

(a) How many legs does the centipede have in a segment?
(b) Does it have wings?
(c) What type of eyes does it have?
(d) How many body parts can be seen?
(e) Does it have antennae? If so, how many?
(f) Where do centipedes live?
(g) In what way are they similar to diplopods?

Main characteristics of organisms in class Chilopoda

1. They have flat bodies with the legs positioned on either side of the body.
2. They have a pair of legs in each segment.
3. Their body is divided into a head and a segmented trunk. However, they have 15 -21 segments, which are fewer than those of animals in the class Diplopoda.
4. They are carnivorous. They use their poison claws to kill their prey.
5. They may have compound eyes, simple eyes or no eyes.

6. They breathe through spiracles found on each side of the body seents.

 Economic importance of arthropodsArthropods have both advantages an ddisadvantages.
Activity 1.15: Discussing the importance of Arthropods Team up with your class member and
come up with a table like the one shown below.
Table 1.5 Economic importance of arthropods

1. Some arthropods are useful to us in many ways. They include:
• Butterflies and bees act as pollinators of flowering plants.
• Bees make honey.
• Lobsters and prawns are used as food.
2. However, most arthropods are harmful to other living organisms.

For instance:
• Ticks transmit diseases in animals; for example East Coast Fever
• Mosquitos transmit malaria.
• Tsetse flies transmit trypanosomiasis in human beings and Nagana in cattle.

• Aphids destroy crops such as maize, coffee and cassava in the fields while weevils destroy stored grains.
3. Sme arthropods cause harm and injury to human beings as well. Some are poisonous if they bite, for example, spiders, wasps, centipede and crabs.