What is the largest sea creature ever?

Answer 1

The blue whale is considered the largest sea creature to exist or have existed, at up to 108 feet in length (33 m) and weighing up to 200 tons (180,000 kg).

Claims of extraordinary Giant Squid (Architeuthis) up to 147 feet long (45 m) are unsubstantiated. The giant sauropod dinosaur Bruhathkayosaurus, which is known only from a few bones, may have equalled the blue whale with a length of up to 110 feet (34 m) and a weight of 175 tons.

Answer 2

a really big monster that lives in the sea.