Lucadia is known as the Guardian of the Sea or the Guardian of the Ocean. He takes on the form of a large draconic sea-serpent in all of his appearances; in Wild Arms 5, there is also a tan-skinned sea nymph literally attached to him. In Wild Arms, Lucadia can be found in a whirlpool blocking exit from the Inner Sea and in Wild Arms: Alter Code F, the Guardian of the Sea can be found underwater in the Shrine of Dragons.
While he is a summonable Guardian in the original Wild Arms, he is merely relegated to the role of a disposable NPC as Lady Harken ends his life when the team is talking with him. Oddly, the remake has him appear as a talking sphere of water; likely he is inside the sphere but chooses not to emerge from it when addressing Cecilia and the others.
In Wild Arms 5, summoning Lucadia fully restores the party instead of damaging the enemy with a tidal wave. This is largely due to the Sea medium being largely associated with healing abilities. Interestingly, Lucadia actually devours the summoner during the sequence and heals them within his confines at the behest of the sea nymph.