Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body. An appendage is any of the homologous body parts that may extend from a body segment. These include antennae, mouthparts, gills, walking legs, swimming legs, sexual organs, and parts of the tail. Typically, each body segment carries one pair of appendages.
An appendage which is modified to assist in feeding is known as a or gnathopod.
Appendages may become uniramous, as in insects and centipedes, where each appendage comprises a single series of segments, or it may be biramous, as in many crustaceans, where each appendage branches into two sections. Triramous appendages are also possible.
All arthropod appendages are variations of the same basic structure, and which structure is produced is controlled by "homeobox" genes. Changes to these genes have allowed scientists to produce animals with modified appendages, such as legs instead of antennae.
