Sea monsters are sea-dwelling mythical or legendary creatures, often believed to be of immense size.
Marine monsters can take many forms, including sea dragons, sea serpents, or multi-armed beasts; they can be slimy or scaly, often spouting jets of water. Often they are pictured threatening ships. The definition of a "monster" is subjective, and some sea monsters may have been exaggerations of scientifically accepted creatures such as whales, and types of giant and colossal squid.