Woodcut of three mythical sea creatures from Hortus Sanitatis printed by Jacob Meyderbach, 1491. Sea cow, sea dog, and sea horse, Small sharks were given the name sea dogs or dogfish, because they have sharp teeth, and popular imagination made them the nautical equivalent of dogs. 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.