Marine mammal Dugong dugong of the order Sirenia (sea cows), found in the Red Sea, the Indian Ocean, and western Pacific. It can grow to 3.6 m/11 ft long, and has a tapering body with a notched tail and two fore-flippers. It has a very long hind gut (30 m/98 ft in adults) which functions similarly to the rumen in ruminants. It is largely herbivorous, feeding mostly on sea grasses and seaweeds, and is thought to have given rise to the mermaid myth.

Previously thought to be the only truly herbivorous marine mammal, Australian research 1995 showed that some dugongs eat sea squirts, which make up 25.5% of the wet weight of faeces from dugongs in Moreton Bay, eastern Australia.

They are slow breeders: the gestation period is 13 months, with up to three years between pregnancies. Dugongs along the Great Barrier Reef are in decline, with the population falling from 3,479 in 1987 to 1,682 in 1994. A survey released 1997 revealed that gill nets used by commercial fishermen kill so many dugongs that their future in this region is in doubt. The Great Barrier Reef Ministerial Council is considering new measures aimed at protecting the animals.