In invertebrate biology, an appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body (in vertebrate biology, an example would be a vertebrate's limbs). It is a general term that covers any of the homologous body parts that may extend from a body segment. These include antennae, mouthparts (including mandibles, maxillae and maxillipeds), wings, elytra, gills, walking legs (pereiopods), swimming legs (pleopods), sexual organs (gonopods), and parts of the tail (uropods). Typically, each body segment carries one pair of appendages.