An encounter between a diving guide and a strange creature on the Great Barrier Reef is being described by marine biologists as the first documented sighting of a Russell’s oarfish on Australia’s eastern coast. Tahn Miller, a master reef guide with Wavelength Reef Cruises, spotted the rare fish.

“It had a mirror finish, like perfectly polished silver, and was as straight as an arrow, almost having the initial appearance of a newly forged sword,” Miller told Stuff. “At that moment, I felt like the ocean had delivered a secret treasure to us.”

Considered the world’s longest bony fish, oarfish can grow to 26 feet in length. The one Miller encountered while leading a diving tour on Opal Reef, which is part of the Great Barrier Reef, was a juvenile. It measured about 16 inches long. An adult oarfish’s giant, snake-like body has led some to speculate that the species is a source of ancient sea serpent myths. In Japanese folklore, oarfish are known as ryugu no tsukai, which translates to “the messenger from the sea dragon god’s palace.”

Long, silvery, and with a crimson dorsal fin running the length of their bodies, the scaleless, ribbonlike filter-feeders make a striking sight on the rare occasions they’re seen alive. More often, the deep-sea fish turn up dead, as a 12-footer did earlier this year in New Zealand

Miller originally posted the video of his sighting on a Reddit thread. He called it an “INCREDIBLE RARE SIGHTING.” Commenters compared the juvenile oarfish to a sewing needle with thread, a wizard’s wand, and “a swordfish’s nose that broke off and gained sentience.” 

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In a second clip that he dubbed “the first video in the world of a juvenile oarfish interacting with a human,” Miller filmed a momentary flash of silver as the creature twirled gracefully through the water when another photographer swam near it. Oarfish typically live in water depths exceeding 2,700 feet. Scientists have not offered an explanation for why the juvenile oarfish was seen swimming in far shallower depths at Opal Reef.