An arthropod is an invertebrate animal having an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda, which includes insects, arachnids, myriapods, and crustaceans. The term Arthropoda as originally proposed refers to a proposed grouping of Euarthropods and the phylum Onychophora. They are distinguished by their jointed limbs and cuticle made of chitin, often mineralised with calcium carbonate. The arthropod body plan consists of segments, each with a pair of appendages. In order to keep growing, they have to go through Moulting, which sheds their skin. Arthropods are bilaterally symmetrical and their body possesses an external skeleton. Some species have wings. They are an extremely diverse group, with up to 10 million species.
