Sirenians are a group of aquatic mammals that include the manatee (7 letters) and the seacow (6 letters). They are also known as sea cows and are found in tropical and subtropical waters around the world. They have large bodies, paddle-like flippers, and no hind limbs. They feed on aquatic plants and can live up to 60 years. They are considered vulnerable to extinction due to hunting and habitat destruction.