What is the medium sized marine animal that is part of the order of placental mammals?
Dugong The dugong ( , ; "Dugong dugon") is a medium-sized marine mammal. It is one of four living species of the order Sirenia, which also includes three species of manatees. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow ("Hydrodamalis gigas"), was hunted to extinction in the 18th century. The dugong is the only strictly marine herbivorous mammal.
Holothuria Holothuria is a genus of marine animals of the family Holothuriidae. Members of the genus are found in coastal waters in tropical and temperate regions. They are soft bodied, limbless invertebrates that dwell on the ocean floor. They resemble a cucumber in form.