The first regional variant discovered amongst Ultra Beasts, the Marine Arrakayit lives in the seas of Ultra Desert. The current favored hypotheses are either that they adapted to water after accidentally digging too far and falling into the ocean, or that they were originally aquatic and burrowed their way into the sands to seek out new food sources. Regardless of their true origin, they are as well adapted to the water as their cousins are to the sand. Their feelers detect currents and bioelectricity, their legs have grown into fins, and their thrashing creates whirlpools rather than earthquakes. Despite all these differences, their behavior is remarkably similar to their land counterparts, including breaching behaviors. Notably, the marine variant of Arrakayit prefers to hunt using the ambush method rather than the pursuit method favored by UB Sandworm.
Marine Arrakayit's most striking difference from its cousin is its vibrant coloration. By living in water instead of sand, Arrakayit gains access to the sense of sight. The aquatic form has fully functional eyes with ten unique color cones that let it see far beyond the visual spectrum. Individuals have been observed displaying to each other by waving their legs and antennae. Their colorful carapaces make them instantly recognizable to other Marine Arrakayit, and they are much more likely to solve territorial disputes through threat displays rather than violence.
Marine Arrakayit are notably better parents than their cousins on land. While their counterparts lay their eggs and leave them to fend for themselves until they hatch, the oceanic parents carry their clutches on their bellies. Hatchlings swim alongside their parents until they are large enough to survive on their own, feeding on the scraps dropped from the jaws of their progenitors. Once they reach an appropriately gargantuan size, they stake out their own territories amongst the corals and crystal formations.
Little else is known about the marine variant. Research on terrestrial Arrakayit is not sufficient to begin in-depth analysis of the sea worms. Hunting Arrakayit also pose a major threat to diving expeditions, and as such other sea life living on Ultra Desert is very difficult to study. Full understanding of the land species is currently prioritized above the study of the sea.