Kingdom Animalia, Phylum Chordata, Class Mammalia, Order Sirenia, contains two families. The dugong has its own family and the three species of manatee have their own family. Order Sirenia only contains four known, living species. These species include the dugong, the Amazonian manatee, the West Indian manatee, and the West African manatee. There used to be fifth species called the Steller's sea cow, but it was hunted to extinction by explorers in the 1700s. Sirenians are now classified as endangered species. Sirenians are mammals so they have complex organ systems, way more advanced than a worm or a beetle. Sirenians reproduce sexually and give birth to live young and have a gestation period of 13 months, or 1 year and 1 month. Manatees only have one young per birth, and they usually wean their young anywhere from 1 to 3 years. Sirenians have a life span of over 30 years and possibly up to 60 years. They have no specific breeding or calving season. Their youn are usually born in the shelter of backwater. Calves are born dark-colored and can swim and surface on its own within half a day of being born. The calf rides on its mother's back, and begins to eat some vegetation by three months of age. Sirenians may be active throughout the day or night. Within a 24-hour period, adults have been observed to feed for 6-8 hours in 1-2 hour intervals, resting for 6-10 hours of the remaining time. A manatee rests by hanging suspended just below the surface of the water or by lying prone on the bottom. In these positions it sleeps, eyes closed and body still. Most feeding occurs between the surface and a depth of 4 meters/ 13 feet. Manatees normally cruise at speeds of 3-7 kmph/ 1.8-4.2 mph, although when pressed they can move up to 25 kmph/ 15 mph. The large tail flipper is the main source of swimming power, providing the forward motion as well as serving as a rudder, which it uses to change direction. The average time a manatee is submergesd is about 260 seconds (4.3 minutes), although a dive lasting 980 seconds(16.3 minutes) was recorded. Sirenians are a nomadic species, meaning that they will move from place to place. Manatees "wander" over hundreds of kilometers in order to meet their dietary requirements. But Sirenians only eat sea grass and other aquatic vegetation. Unlike other marine mammals, sirenians have an extremely low metabolism and zero tolerance for cold water. Like dolphins and whales, manatees and dugongs are totally aquatic mammals that never leave the water - not even to give birth. The combination of these factors means that sirenians only like to live in the warm shallow coastal waters, estuaries, and rivers, with healthy ecosystems that support large amounts of sea grass and/or aquatic vegetation. Ironically, humans may be the only chance manatees and dugongs have to survive. In every country where manatees and dugongs live, there are people and organizations working to protect the Sirenians. In the United States today there is expected to be anywhere from 1000 to 2000 or less manatees in existence today. This is why it is important we protect this endangered species. Sources: Books Allen, Katy Z.; Berg, Linda Ruth Ph.D.; Dumas, Leila; Dushek, Jennie and Taylor, Mark F. Ph.D. Holt Science and Technology: Life Science 200l Internet Myers, Phil "Animal Diversity Web: Online Available http://animaldiversity.ummz.umich.edu/site/accounts/information/Sirenia.html 2005 Pictures http://cars.er.usgs.gov/Education/sldshw/manatee/Image3.html http://cars.er.usgs.gov/Education/sldshw/manatee/Image4.html http://cars.er.usgs.gov/Education/sldshw/manatee/Image8.html Author: Tanner O. Date Published: April 2006"