Sea Serpents

Dragons not only live on land and in the air, but also in the sea. The Sea Serpent is a Dragon, perfectly adapted to water. It attacks ships on sea with its fire breath and magic abilities. Intelligent, they stay at a distance for their own safety. Warriors are helpless against this kind of attack, and have to trust the ship's cannons to deal with the foe.

Sea Serpents logically are only encountered at sea.

Sea Serpents stayed the same after Ultima IV, however, in Ultima IX, they did a strange transformation away from the serpent form, with no explanation at all.

Variations
In various Ultimas, sea serpents have appeared in one form or another.

In Ultima I the Ness Creature appears (mention is made in the U1 guidebook about the creatures having been verified by this stage), but they do not breath fire or use magic. They re-appear in Ultima II as "Sea Monsters," still with no special abilities.

The creatures first called Sea Serpents appeared in Ultima III, wherein they first displayed the ability to hurl magic at their enemies.

In Serpent Isle the conventional sea serpent is replaced by its cold-water cousin, the Frost Serpents, which are almost identical, other than the fact that the creature is blue, and spits cold-fire instead of normal fire.