As an adjective herbivorous
is feeding chiefly on plants.
As a noun sirenian is
(zoology) any of a group of aquatic, herbivorous mammals, of the order sirenia
, including the manatees and dugong.
(zoology) Any of a group of aquatic, herbivorous mammals, of the order Sirenia , including the manatees and dugong.
*2011 , Richard Shelton, "Sheep, pig, whale", Times Literary Supplement , 22 Sep 2011:
*:The cetaceans (whales and dolphins) together with the sirenians (sea cows and manatees) are the sea mammals best-adapted to the seas of today, but it is the cetaceans that have most engaged the attention of mankind as both prey and fellow sentient being.