The phylum Arthropoda is the largest and most varied in the animal kingdom. It includes well over one million described species. This represents approximately three-quarters of all known biological organisms, living or extinct. Countless arthropods remain undescribed (not yet named and studied), and the actual number of living species could be as high as ten million or more. Some of the more well-known arthropods include insects, crustaceans, and spiders, as well as the fossil trilobites. Arthropods are found in virtually every known marine (ocean-based), freshwater, and terrestrial (land-based) ecosystem, and vary tremendously in their habitats, life histories, and dietary preferences.

Characteristics of Arthropods

Despite the remarkable variety of arthropod species, all share aspects of a single basic body plan. All arthropods possess a stiff exoskeleton (external skeleton) composed primarily of chitin. In some species, lipids, proteins, and calcium carbonate may also contribute to the exoskeleton. The external skeleton...