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.
Verticordiidae Verticordiidae is a taxonomic family of very small saltwater clams, marine bivalve molluscs in the order Pholadomyoida.