Monstrum Marinum effigie Monachi (Monster of the sea forms Monk) from Ulisse Aldrovandi's Monstrorum Historia, 1642. The sea monk, or sometimes monk-fish, was the name given to a sea animal found off the coast of Denmark in 1546. 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 and are often pictured threatening ships or spouting jets of water. This particular sea monster