Arthropods are the largest phylum on earth and the most diverse. They are invertebrates like all of the animals we studied last week, but there are so many, and they have some major differences from the other (simple) invertebrates we looked at last week.

Arthropods have the following features:

• exoskeleton made of chitin
• jointed appendages
• segmented body parts
• open circulatory system
• sensory organs
• most have compound eyes

The exoskeleton of the arthropods serves a variety of functions. It can protect the body and it must be shed in order for the organism to grow, it is very stiff and hard. 

There are five groups of arthropods:

• Trilobites - these arthropods are now extinct
• Crustaceans - this includes crabs, lobsters, crayfish, isopods, barnacles, and even pill bugs
• Chelicerates - horseshoe crabs, arachnids, scorpions, mites and ticks
• Hexapoda - insects and their relatives (ants, bees, butterflies, moths, cockroaches, flies and mosquitoes)
• Myriapoda - centipedes and millipedes. 

Complete the tasks on the list below:

• Go to this page, http://cnx.org/contents/GFy_h8cu@10.53:OUA71yUo@7/Superphylum-Ecdysozoa, and start reading with the following section(s):
• Phlym Arthropoda - Read until you get to Subphylum Crustacea 
• Use the Glossary at the bottom of the page to help with the vocabulary for this week
• Use the Review Questions and Free Response questions to check for understanding

Download for free at http://cnx.org/contents/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.53