The identifying characteristic of arthropods are their jointed appendages. They have a nervous system that includes a brain and several cords of nerve tissue. Their bodies are also segmented. Arthropods must regrow their exoskeletons by molting. They also have a complex muscular system.

There may be as many as 30 million species of arthropods.

One example is the yellow sac spider, also known as Cheiracanthium punctorium. This animal's sting is sometimes more powerful than a wasp sting.

Another example is the house centipede, also known as Scutigera coleoptrata. This animal may grow up to 15 pairs of legs.

http://www.oceanicresearch.org/education/wonders/arthropods.htm

http://animaldiversity.ummz.umich.edu/accounts/Arthropoda/