Unit 2 Section 9  - Arthropods

Part a| Part b | Project and Dissection lab | Key terms | Review | Section quiz | Quizstar

  1. Arthropod
  2. Exoskeleton
  3. Molting
  4. Compound eye
  5. Simple eye
  6. Open circulatory system
  7. Crustacea
  8. Copepod
  9. Decapod
  10. Antennule
  11. Antenna
  12. Mandible
  13. Maxilla
  1. Maxilliped
  2. Cheliped
  3. Swimmeret
  4. Uropod
  5. Cephalothorax
  6. Abdomen
  7. Gill
  8. Green gland
  9. Arachnida
  10. Chelicera
  11. Pedipalp
  12. Diplopoda
  13. Millipede
  1. Chilopoda
  2. Centipede
  3. Insecta
  4. Metamorphosis
  5. Larvae
  6. Pupa
  7. Chrysalis
  8. Cocoon
  9. Nymph
  10. Warning coloration
  11. Mullerian mimicry
  12. Batesian mimicry

Phylum Arthropoda

click to find the answer to today's question How can an insect nymph be distinguished from an adult?

The phylum name means jointed foot. Jointed appendages is a major characteristic of all members of the phylum. The following are also traitslink to a local webpage found in most arthropods:

All arthropods have an exoskeleton.

Once it is formed, this hard body covering does not grow. To allow for growth, arthropods have to shed their exoskeleton in a process called molting.
Most arthropods have compound eyes link to a local picture composed of many individual lenses.
In addition to the compound eyes, many arthropods also have single lens, simple eyes that sense light intensity.
All arthropods have an open circulatory system.
This type of system has a heart and a few major arteries veins. There are very few capillaries connecting the arteries and veins. The blood spills into the body cavity where it is picked up and taken back to the heart. Arthropods are limited in size because of this inefficient circulatory system.

Subphyla of arthropods: link to an Internet Website

Crustacea - members have mandibles (chewing mouthparts) and branched antennae.

Uniramia - members have mandibles and un-branched antennae.

Chelicerata - members have chelicerae (pincher-like mouthparts) and no antennae.

Horseshoe crab - which subphyla do they belong to?

There are some 40,000 species in the subphylum Crustacea, ranging in size from copepods link to a local picture and water fleas link to a local picture that are just large enough to be seen with the unaided eye, to shrimp link to a local picture that you might enjoy as food, to crabs, link to a local picture some with a leg span of over 12 feet. The crayfish link to a local picture is a freshwater crustacean in a group called decapods. Decapod means "ten feet", indicating that they have five pairs of legs.

Crayfish of the world: link to an Internet Website

Appendages of the Crayfish
Walking Legs
touch, taste, and equilibrium
touch and taste
manipulate food and draw water over the gills
touch, taste, and manipulate food
defense and capture food
movement over solid surfaces
create water currents and transfer sperm

Other Crayfish Structures
  • The body is divided into two major sections:
      Cephalothorax - the head (5 segments) and thorax (8 segments).
      Abdomen - (six segments and Telson).
  • Gills are used for respiration. Feather-like gills, located in a chamber under the carapace, are attached to the base of each walking leg.
  • The green gland is a excretory organ used to remove excess water from the body.
  • There is a system of thousands of small sensory hairs covering the exoskeleton that help the crayfish sense vibrations and chemicals in the water.
  • The two compound eyes, composed of more than 2000 lenses, are set on short, movable stalks.
  • The separate sexes are distinguished by the first pair of swimmerets. The males have a stiff, elongated pair of swimmerets that are used to transfer sperm to the body of the female. All the swimmerets of the female are soft and used to carry the fertilized eggs and newly hatched young.


Assignment  2.9a - Arthropods
  1. Right click on this(Arthropods) and "save target as" to you desktop. After video has downloaded watch video and complete short quiz at the end. Write your answer here.
  2. Why is this phylum named the arthropods?
  3. What are the phylum characteristics?
  4. Does the arthropod circulatory system differ from that of the Annelida? Explain.
  5. Which arthropod subphylum are crayfish classified under?
  6. What is the scientific name for a crayfish that is found in Arizona?
  7. List the common and scientific name of one member each from the Uniramia and Chelicerata subphyla.
  8. Cut and past into word (or draw) a external and internal diagram of a crayfish. Label as many parts as possible (Do not cut and paste a crayfish that is already labeled). Crayfish must be labeled by you.

Honors biology:  complete the above section along with the following section.

  1. Research one specific arthropod (not a crayfish) and list the common and scientific name. Summarize all important characteristic about your arthropod (habitat, reproduction, niche, feeding, movement, body parts, region found, interesting facts, etc).


Section 9 part b Arthropoda


Other arthropods:

Class Arachnida: subphylum Chelicerata

The largest class in the subphylum Chelicerata contains more than 70,000 species including ticks, mites, spiders, and scorpions. Arachnids have a body divided into a cephalothorax and abdomen. The cephalothorax usually bears six pairs of jointed appendages: one pair of chelicerae (fangs), one pair of pedipalps (hold and chew food), and four pairs of walking legs.

Scorpions link to an Internet Websiteare a familiar site in Arizona. The bark scorpion has a very toxic venom.

Ticks link to an Internet Website carry some serious diseases and should be regarded with caution.
In Northern Arizona, mites called chiggers link to an Internet Website can cause a lot of discomfort.
All spiders are poisonous.
Most spiders are not aggressive and their bite is no worse than a bee sting.

Only two spiders in the U.S. have bites that are normally harmful to humans.

Class Diplopoda: millipedes, subphylum Uniramia. link to an Internet Websitelink to an Internet Website link to a local picture

Two pairs of weak legs per body segment.
Slow-moving with a rounded body.
These plant-eating animals do not have a sting.
When threatened, they coil up and secrete a noxious fluid containing cyanide.

Class Chilopoda: centipedes, subphylum Uniramia. link to an Internet Website link to a local picture

One pair of strong legs per body segment.
Fast-moving with a flattened body.
These carnivorous animals have a pair of poison jaws, not a stinger.

Class Insecta: link to an Internet Website insects, subphylum Uniramia.


The body of an insect is divided into three parts:

Exoskeleton - hard body covering

Go through metamorphosis

Keys to the Orders of insects.link to a local webpage
click for a career
Local links to insect drawings:


All insects go through one of two types of metamorphosis:

Insect defensive adaptations:

The grasshopper is generally used as a "typical" insect for anatomy study.

Head lice link to an Internet Website are also insects.


Test your knowledgelink to an Internet Websiteof insects and spiders.



Assignment 2.9b - Arthropods


2.9b part 1

  1. Paste this grasshopper diagram link to a local picture onto a Word document, enlarge and label the following parts. Below the diagram give a brief definition of each part.

    • Head
    • Thorax
    • Abdomen
    • Antenna
    • Mouth
    • Walking Legs
    • Forewing
    • Hindwing
    • Spiracles
    • Jumping Legs
    • Spines
    • Hooks

  2. Paste this grasshopper diagram link to a local picture onto a Word document, enlarge and label the following parts. Below the diagram give a brief definition of each part.

    • Gizzard
    • Aorta
    • Gastric Ceca
    • Brain
    • Ventral Nerve Cord
    • Tracheae
    • Colon
    • Ovary
    • Esophagus
    • Salivary Glands
    • Rectum
    • Malpighian Tubules
    • Oviduct
  3. Find a diagram of the mouth parts of a grasshopper and label the: labium, labrum, maxilla, clypens, palps and mandibles.

2.9b Part 2

  1. How can an insect nymph be distinguished from an adult?
  2. How do chiggers cause discomfort to humans?
  3. Briefly describe what will happen if a human is stung by a black widow.
  4. Briefly describe what will happen if a human is stung by Centruroides exilicauda or sculpturatus.
  5. Click on this scorpions link link to an Internet Website. Read the information and test your comprehension by taking the quiz linked at the bottom. How did you do? Cut and past your results here.
  6. There are 25 - 30 different species of scorpions in Arizona. Examine these photos (A)link to a local picture (B)link to a local picture (C)link to a local picture of the most venomous, the most common and least common scorpions found in Arizona. Using the pictures find the common and scientific names of each (finding a identification key will be helpful).
  7. In Arizona we often find scorpions in and around homes. Can you identify a Bark scorpion? Use this link link to an Internet Website to find and list all the characteristics use to identify this type of scorpion.
  8. Compare and contrast complete and incomplete metamorphosis, is there a benefit to either?
  9. What type of defenses have insects developed? Explain.
  10. Briefly describe what head lice is and how you can get it and get rid of it.
  11. Name the Arizona state insect. What arthropod class does it belong to?
  12. Identify the order to which each of the following insects belongs: (see key to orders above)
    • butterflies
    • flea
    • grasshopper
    • house fly
    • walking stick
    • earwig
    • moths
    • mosquito
    • fire ant
    • cicada
    • stink/squash bug
    • termite
    • killer bee

Honors biology: Include these questions with the day 2.9b part 2 assignment

  1. Briefly describe Forensic Entomology.
  2. What can a forensic entomologist find out about a homicide? Explain how this is done?
  3. Using the forensic entomologist (science career) link above read case no. 1 and answer the following questions.


Research Links: