Teleosts are distinguished for their tails and their jaws. Their tail fins (caudal fins) are fully homocercal (symmetrical), with two equally-sized lobes that extend from the end of the spine. Teleosts also have a highly mobile mouth parts. The bones of the upper jaw, the maxilla and premaxilla, are fully movable and this bone structure enables them to protrude their jaw outward from their skull when opening their mouth).