Woodcut from Gesner's great zoological work, Historiae animalium, 16th century.The fearsome Ziphius, with a face looking like a cross between an owl's and a worried human's, endures a bite from a porcine sea monster while munching on a hapless seal. The Ziphius might have been based on a killer whale or great white shark. 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.