Arthropods are animals belonging to the Phylum Arthropoda and include the insects, arachnids, crustaceans and others. Arthropods are characterized by the possession of a segmented body with appendages on at least one segment. They have a dorsal heart and a ventral nervous system. All arthropods are covered by a hard exoskeleton made of chitin, a polysaccharide, which provides physical protection and resistance to desiccation. They are the largest phylum in the Animal Kingdom with more than a million described species making up more than 80% of all described living species, and a fossil record reaching back to the late proterozoic era. Arthropods are common throughout marine, freshwater, terrestrial, and even aerial environments, as well as including various symbiotic and parasitic forms. They range in size from microscopic plankton up to forms several metres long. Reference Wikipedia.
