The seasaur is a large aquatic monster, similar to the mythological Leviathan. Most of its body is blue, with grey undersides, and orange on its fins and the webs on its limbs. It also has a pair of long, pale green horns on its head. Seasaurs are dangerous monsters to face on the open seas, being able to breath out powerful fire and ice attacks at seafaring adventurers. In their first appearances, they were stronger than abyss divers, but starting with Dragon Quest VIII, they became the weaker monsters.
The seasaur's original Japanese name Gyaōsu (ギャオース,Gyaōsu?) is inspired by the kaiju Gyaos featured in the 1967 Japanese film Gamera vs. Gyaos. However, in the movie, Gyaos is a giant bat or pterosaur-like creature with leathery wings, rather than a sea monster. Over the years, Gyaos's appearance has become more draconic, with larger wings.