1. Arthropods

2. What is An Arthropod? Phylum Arthropoda
Insects, crabs, centipedes, and spiders are all in this group.
Arthropods have a segmented body, a tough exoskeleton, and jointed appendages.
An exoskeleton is a tough outer covering. It is made from chitin. Exoskeletons can be very different in different animals.
Many land arthropods have a waxy layer over its exoskeleton to prevent water loss.
Appendages are structures like legs and antennae that extend from the body.

3. Form and Function in Arthropods
Arthropods have many different ways of getting food. There are herbivores, carnivores, and omnivores, as well as, bloodsuckers, filter feeders, detritivores, and parasites.
They have many different mouth parts, depending on what they eat.

4. Respiration
Most terrestrial arthropods breathe with tracheal tubes. Air enters and leaves through spiracles, small openings along the body.
Spiders use book lungs – the lungs have layers of tissue that look like a book.
Aquatic arthropods have gills.

5. Circulation and Excretion
Arthropods have an open circulatory system.
They have a well developed heart
Many land arthropods have malpighian tubes for excretion. These remove waste from the blood and then the arthropod is able to get rid of it.

6. Response and Movement
All arthropods have a brain. Most arthropods also have a very good sense of smell.
They have well developed muscles. The exoskeleton is a place for the muscles to attach.

7. Growth and Development
An exoskeleton does not grow as the animal grows. Arthropods have to go through molting. This is when it sheds its exoskeleton to make a new, larger one.
The process is: when an animal is ready for a new exoskeleton it will shed its old exoskeleton. While the new exoskeleton that has started forming is still soft, the animal will fill with air or fluids to make the new exoskeleton larger so the animal has some room to grow.
Most arthropods molt several times between hatching and adult.
The animal is very vulnerable to predators when it has a soft exoskeleton so it may hide during this time.