Seahorses

Seahorses... these graceful, appealing ocean creatures have nasty personalities. They enjoy shooting foes at range, which they do very effectively. They are also rather strong, flexible, even intelligent, and they take a fair amount of punishment to be defeated. This makes them dangerous foes.

As the name says, they are found at sea.

Lore
''These magical creatures appear quite fair and are not evil, but if offended they make devastating enemies. They are possessed of powerful magical abilities which can wreak havoc among thy party.''

- from "The History of Britannia", Ultima IV

''These graceful, appealing ocean creatures have nasty personalities. They enjoy shooting foes at range, which they do very effectively. They are also rather strong, flexible, even intelligent, and they take a fair amount of punishment to be defeated.''

- from "Book of Lore", Ultima V