In animal biology, an antenna is usually one of a pair of many-jointed, whip-like structures present on the head of many arthropods, particularly insects (first appendage on head) and crustaceans (second appendage). Antennae have a sensory function, though in some crustaceans they are used for attachment or swimming. The first segment of an insect's antenna is known as a scape. It has muscles and pivots on a point called the antennifer, thus enabling the antenna to be moved in any direction.