Arrakan was home to Leviathans.[1]
Behind the scenes
Arrakan was first introduced in the unlicensed roleplaying adventure "Flight of the Jedi", which is considered non-canon due to a lack of Lucas Licensing approval.
Non-canon content
Arrakan was a water world in the Sulphis system of the Outer Rim, on the opposite side of Celanon from Lennax. Its name meant the Blue Pearl. Arrakan's skies were filled with violent atmospheric storms and glowering clouds connected to the water surface by "vast whirlwind twisters of air and water."
The indigenous Battrachs maintained a floating harbor at a coral-like island, where starships landed in moored giant bivalves, which then closed their shells and carried the craft to the underwater capital city, Kearleonis. Animals could travel underwater in giant jellyfish. The Battrachs, the bivalves, and the jellyfish were all genetically engineered by the indigenous Duors, who themselves believed they had been made by a millennium-old Leviathan named Kithnarrock.
Kithnarrock was a contact for the Alliance to Restore the Republic. A number of survivors of the Great Jedi Purge contacted the Alliance through Kithnarrock; however, this resulted in an Imperial fleet attacking Kithnarrock.
Appearances
Non-canon appearances
"Flight of the Jedi" — Valkyrie 19–20 (First appearance) (Unlicensed)- Star Wars: Jedi Mind Tricks
Sources
Drawing from the Imagination: Mythological Creatures in Star Wars, Part 1 on StarWars.com (backup link) (original link is obsolete) (First canonically mentioned)