There are four species in this order and they are all endangered or threatened. They are distantly related to elephants! Sirenians live in tropical and sub-tropical rivers, estuaries, and coastal waters. They live their entire lives in the water. They have large, thick bodies with flippers instead of arms. They have no visible hind limbs, although they do have two hind limb bones hidden in muscle inside their bodies. Their tail is a flattened rear flipper that they use like a paddle to propel themselves through the water. They have thick, gray skin covered with a little hair. They have small eyes and nostrils on the top of their snouts that they use to take in air. Sirenians are herbivores and eat aquatic plants.