Arthropos are animals belonging to the Phylum Arthropoda (from Greek ἄρθρον arthron, "joint", and ποδός podos"foot", which together mean "jointed feet") and include the insects, arachnids, crustaceans and allies. 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. Arthropods grow by shedding this covering in what are termed molts.