haha nice question. its a whale. or maybe a shark.
A plant-eating mammal that lives under the sea is commonly known as a sea cow or a manatee.
Bottomki
sea lions
Manatees and dugongs.
sea cow
No its a mammal but it lives in the sea and then comes up for air above the surface of the ocean.
An otter is an aquatic mammal.
Walrus
A mammal can live on land and in the water, or sea.
do you mean dolphin? (as in the mammal smaller than a whale that lives in the sea)
Dolphin
The only mammal that can fly is the bat, so that must be the answer.