The sea creature is a mysterious amphibian who dwells at the bottom of the Java Sea.
It is described by Dr. Quest as a cross between a Manticore and Hippocampus (two "mythical monsters"), and compared by Race to a dinosaur; the cook, Charlie, describes it as a "dragon." Though the Captain of a Dutch freighter guesses that it is a deep-sea creature due to its large eyes and its dislike of bright light, it is nevertheless air-breathing, and therefore probably rises to the surface from time to time (though in this case, the captain implies that it was driven to the surface by a storm). The creature's skin is apparently impervious to gunshot, and it is described as having enormous strength.
The creature attacks the Dutch freighter Star of Borneo and kills a number of crewmen, driving the others away. Driven by curiosity or fear, it destroys the Quests' plane after it lands on the ship. The Quest team manages to hold it off with lights and acetylene torches; the creature mounts to the top of the ship's mast and, hit by a harpoon fired by Charlie, the monster makes a spectacular dive into the water, presumably returning to the depths of the sea.
- Dr. Quest's comparison of the Sea Haunt to a manticore is not particularly apposite, as the manticore is generally described as lion-like in form with a human-like face; however, it is sometimes said to have multiple rows of teeth, and it may be this feature Dr. Quest had in mind.
- Dr. Quest is considerably more on target with his comparison of the creature to a hippocampus, since that is simply the ancient name for a sea-horse, and is in fact sometimes used today for the actual fish, though in ancient times it was thought of as a sort of horse with a mermaid-like tail and webbed flippers instead of fore-hooves.
- Charlie's description of the Sea Haunt as a "dragon" may reflect the fact that in old Chinese folklore, dragons were many times thought of as aquatic creatures, often possessing power over water, rainfall, typhoons, and floods.
- If the Sea Haunt is actually a deep-sea creature, it is surprising that it can both climb and high-dive with great agility, since creatures living primarily underwater rarely have such skills.