any of an order (Sirenia) of large, vegetarian sea mammals with a cigar-shaped body, a blunt snout, large, mobile lips, flipperlike forelimbs, and a tail fluke, consisting of the dugong and manatee
See sea cow in American Heritage Dictionary 4
noun
Any of several large, cylindrical, herbivorous marine mammals of the order Sirenia, having a paddlelike tail and rounded front flippers, including the manatee, dugong, and the very large species Hydrodamalis stelleri of the northern Pacific that became extinct in the late 1700s. Also called sirenian.