Lesson 1.7 Phylum Arthropods

This is a free lesson. We trust you enjoy it!

Introduction to lesson

In the last lesson, you looked at how the animal kingdom is further divided into phyla. You then spent time looking at the phylum vertebrates and the five main classes within that phylum, namely: fish, birds, mammals, reptiles and amphibians. In this lesson, you will explore a very successful phylum - the phylum arthropods. Arthropods are animals with jointed legs.

 This is a fairly long lesson and can be taken over two days. Most of the work should be revision of prior knowledge.

Review of past lessons

Review the characteristics of

  1. birds
  2. reptiles
  3. amphibians
  4. mammals
  5. fish

Preparing for the lesson

Ask yourself the following questions, as you prepare to study arthropods:

  1. What do you think is the largest group of animals?
  2. Why do you think there are so many animals in this group?
  3. Which is your favourite invertebrate animal and why?

Phylum Arthropod

Read the section Phylum arthropods in the Coursebook - p. 11-12. This includes insects, crustaceans, arachnids and myriapods. (Note that each of these are classes of the phylum Arthropod).

Learning Activity 1

  1. As you work through the different classes add them to the visual aid chart you started making in Lesson 1.6 (Learning Activity 7).
  2. Make a section for each of the classes and give the characteristics of each class.
  3. Draw a representative animal for each class (similar to Figures 1.11-1.15) and label your drawing. You may add extra labels not included in the course book.

Learning Activity 2: Phylum Arthropod

Answer the following questions in your exercise book:

  1. What are the two main characteristics of all members of the phylum arthropods?
  2. Why do you think this such a 'successful' or numerous group?
  3. Name four classes of arthropods

Learning Activity 3: Insects

Answer the following questions in your exercise book:

  1. What are the characteristics of insects?
  2. Describe the life-cycle of insects that undergo complete metamorphosis.
  3. Describe the life cycle of insects that undergo incomplete metamorphosis.
  4. What are some of the advantages of metamorphosis?
  5. How many body parts does an insect have? What are they?
  6. What type of eyes do most insects have?
  7. Draw a diagram of an insect (e.g. fly or bee, or butterfly) and label the following: body parts (head, thorax, abdomen), compound eyes, antennae, mouth parts, three pairs of legs, two pairs of wings

Learning Activity 4: Crustaceans

Answer the following questions in your exercise book

  1. What are the characteristics of crustaceans?
  2. What is the habitat of most crustaceans and how have they adapted to such as habitat?
  3. Draw a diagram of a crab and label the following: rostrum, antenna, eye, jointed leg, chelipeds, carapace and exoskeleton.

Learning Activity 5: Arachnids

Answer the following questions in your exercise book

  1. What are the characteristics of arachnids?
  2. What are the differences between the class of insects and the class of arachnids
  3. Draw a diagram of a spider and label the following: body parts (head and cephalothorax), eight legs, simple eyes, spinneret, pedipalp

Learning Activity 6: Myriapods

Answer the following questions in your exercise book

  1. What are the characteristics of myriapods?
  2. What are the differences between myriapods and the phylum annelids and the phylum nematodes?

Learning Activity 7: Comparison table

Copy and complete the following table which compares the different classes under the phylum arthropods.

 ExoskeletonNo. legsNo. wings presentNo. body partsTypes of eyesBreathing apparatus
 Insect (grasshopper)            
 Arachnid (spider)            
 Crustacean (crab)            
 Myriapod (centipede)            

Add the following terms and definitions to your biology reference book:


arthropod - an invertebrate animal of the large phylum Arthropoda, that has an exoskeleton and several pairs of jointed legs, such as an insect, spider, or crustacean.

exoskeleton - a rigid external covering for the body in some invertebrate animals, especially arthropods, providing both support and protection.

thorax - the middle section of the body of an insect, between the head and the abdomen, bearing the legs and wings.

abdomen - the posterior part of the body of an arthropod, especially the segments of an insect's body behind the thorax.

cephalothorax - the fused head and thorax of spiders and other chelicerate arthropods

carapace - the hard upper shell of a turtle, crustacean, or arachnid

chelipeds - one of the pair of legs that bears the large chelae in decapod crustaceans.

pedipalp - each of the second pair of appendages attached to the cephalothorax of most arachnids. They are variously specialized as pincers in scorpions, sensory organs in spiders, and locomotory organs in horseshoe crabs.

book lungs - (in a spider or other arachnid) each of a pair of respiratory organs composed of many fine leaves. They are situated in the abdomen and have openings on the underside.

Add any other term and its definition which you did not know or understand in the text.

Common misunderstandings and misconceptions

Be careful of not confusing the characteristic features of one class of arthropods (e.g. insects) with the characteristics in general. Arthropods is the broad category of animals with an exoskeleton and jointed legs. Then you must know the characteristics of the different groups within that phylum - insects, crustaceans, arachnids, and myriapods.

Do not get confused between the words arthropods and arachnids. Arthropods is the phylum that includes arachnids, insects, crustaceans and myriapods. Arachnid is a class within the phylum arthropods. Arachnids includes spiders, ticks and scorpions.

Closing question

If you were given a biological specimen, what characteristics would you expect to see if the specimen was an arachnid?

Closing the lesson

  • What new things have you learned in this lesson?
  • What did you already know?
  • Is there anything that confuses you? Ask your parents or teacher to help you.