A Whale and I do believe they are also the biggest mammal on earth too.
The Blue Whale is the largest sea creature known to date
The largest and heaviest living creature on earth is the blue whale.
gaint squid was the largest sea creature foun in californian ocean
giant squid
A Whale.
The blue whale is the heaviest creature in the sea (considerably heavier than even the largest dinosaur).
It is the giant octopuss. the creature itself is around 2m long!
killer whale
The largest heart has to be in the largest creature that has ever inhabited the earth, which is the Blue Whale!
The most poisonous creature is the sea snake.
That would be the whale shark.
If your asking which is the biggest animal then a whale is the largest underwater creature and elephants are the largest land mammals