What does "sirenia" mean?

Sirenia: An order of large aquatic herbivorous mammals, including the manatee, dugong, rytina, and several fossil genera. Note: The hind limbs are either rudimentary or wanting, and the front ones are changed to paddles. They have horny plates on the front part of the jaws, and usually flat-crowned molar teeth. The stomach is complex and the intestine long, as in other herbivorous mammals. See Cetacea (b).