This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Sea Monster (Worldwide)
Sea monsters are beings from folklore believed to dwell in the sea and are often imagined to be of immense size. Marine monsters can take many forms, including sea dragons, sea serpents, or tentacled beasts. They can be slimy and scaly and are often pictured threatening ships or spouting jets of water.
The definition of a "monster" is subjective; further, some sea monsters may have been based on scientifically accepted creatures, such as whales and types of giant and colossal squid. Sea monster accounts are found in virtually all cultures that have contact with the sea.