Manatees are spindle-shaped, similar to small whales, but with shorter necks, which are different from whales. It is 2.5 ~ 4.0 meters long and weighs about 360 kilograms. Manatees store a lot of fat under the skin, which can keep their body temperature in seawater; The forelimbs are specialized into paddle-fin limbs without hind limbs, but the degenerated pelvis is still preserved; A flat caudal fin with a large fleshy body; There is hair in the embryo, and the newborn cubs have sparse short hair. When they are adults, their trunks are basically hairless, except for beards around their lips and touching hairs on their heads. The head is big and round, with big lips. Because the neck is short, the head can move flexibly and feed easily. The position of the nostril is above the snout, which is suitable for breathing on the water. There is a valve in the nostril to seal the nostril when diving. The length of the intestine exceeds 20 meters; The stomach is divided into two cavities, the cardia cavity has glandular sac and the pyloric cavity has blind sac. Small eyes and poor eyesight; Good listening. The lung is long and narrow, without pulmonary lobules; The skull is big, but the skull is small and the brain is underdeveloped.