Any member of the largest phylum, Arthropoda, in the animal kingdom.
Arthropoda consists of more than one million known invertebrate species in four subphyla: Uniramia (five classes, including insect s), Chelicerata (three classes, including arachnid s and horseshoe crab s), Crustacea ( crustacean s), and Trilobita ( trilobite s). All arthropods are bilaterally symmetrical and possess a segmented body covered by an exoskeleton containing chitin , which serves as both armour and a surface for muscle attachment. Each body segment may bear a pair of jointed appendages. The phylum includes carnivore s, herbivore s, omnivore s, detritus feeders, filter feeders, and parasites (see parasitism ) in nearly all environments, both aquatic and terrestrial.