What began as a marine science instructor's leisurely snorkeling trip off the Southern California coast turned into the discovery of a monstrous legendary sea creature.

Jasmine Santana, a 26-year-old instructor for the Catalina Island Marine Institute, was snorkeling in Toyon Bay on Sunday afternoon when she saw a half-dollar sized eye staring at her from the sandy bottom. That eye belonged to an 18-foot-long oarfish, a find so rare, the institute hailed it as a "discovery of a lifetime" in a news release.

Crew members from the Catalina Island Marine Institute's Sailing School Vessel Tole Mour holds the 18-foot-long oarfish discovered in Toyon Bay on Sunday, Oct. 13, 2013. Credit: Courtesy Catalina Island Marine Institute

Oarfish are the stuff of myth and legend, likely the stars of sea serpent tall tales throughout history. The longest of the bony fish species, they are rarely seen dead or alive.

Santana, who didn't have a camera with her at the time, decided to bring the massive fish, which was newly dead with the body almost fully intact, ashore.

Credit: Courtesy Catalina Island Marine Institute

"She said, 'I was thinking to myself, there's no way anyone is going to believe me," said Mark Waddington, the senior captain of the institute's sailing school training ship, Tole Mour.

Waddington, one of many instructors who take middle school-age students out on the institute's Guided Discoveries tours, told ABCNews.com that he and a group of instructors were unloading gear from the Tole Mour, when they spotted Santana about 150 feet away, trying to bring in the fish.

"I remember looking over and seeing her wrestling with it," he said. "When I saw the long tail, I thought, 'Oh that's got to be an oarfish.'"

Waddington said he and about 15 to 20 other people from boat rushed over to help Santana, who pulled the monster in 90 feet, before the waves helped push it onto the sand.

When he saw the size of the oarfish for the first time, Waddington said, "I was beside myself, I'm sure I said 'awesome' a lot."

"I had heard of it in studies, but never thought I would see one in person," he added.

Credit: Courtesy Catalina Island Marine Institute

It is believed that oarfish, which can grow to be more than 50 feet long, can dive down to 3,000 feet and usually live in deep parts of the ocean, which is why little has been studied about them. Waddington said in the 35 years of Guided Discoveries talking more than 1 million people out on sea excursions, "this was the first one we've seen of this size."

Tissue samples of the giant were sent to experts at the University of California at Santa Barbara for further study. Although CIMI instructors had hoped to preserve the fish's skeleton, oarfish bones are very delicate, Waddington said, so the specimen remains on ice.

But many other unusual and rare phenomena have occurred in the Toyon Bay this fall, Waddington said. For one, market squid, which are the small variety sold for food consumption, usually come to the bay to mate for a very brief time, but this year, thousands upon thousands of market squid have been staying in the bay for two months straight, which has brought in a variety of dolphins.

Waddington said they have also had four recent green turtle sightings - another rarity.