McGraw Hill
Arthropods
Are spiders related to crabs? Study the order of arthropods with a reading selection about animal diversity. It provides details about each class within the order, as well as vivid pictures and explanatory charts.
BiologyWise
Biology Wise: Classification of Animals
The classification system for animals is explained and examples given. Includes suggestions for how to teach the system to younger students and how to create a classification chart of the animal kingdom.
Wikimedia
Wikipedia: Arthropod
Wikipedia offers information on arthropods, the largest phylum of animals. Includes scientific classification chart and image.