The New Jellyfish Discovered Off the Coast of Japan

It is estimated that there are between 700,000 and one million creatures living in the ocean. To date, approximately 242,500 of those marine animals have been discovered. This means that, in the shallows and depths of the seas worldwide, there are creatures waiting to be found.

One of those animals recently proven to be a new species was a jellyfish discovered off the coast of Japan. As it turns out, the jellyfish were spotted by a teenager with an extraordinary passion for jellies, who not only collected some of the creatures but also helped them thrive in captivity.

The New Jellyfish Were Hiding in Plain Sight

In 2018, Ryoya Sugimoto was a 13-year-old who was enjoying some time by the water at Tanabe Bay in Wakayama, Japan. The then-teen was a jellyfish enthusiast, whose interest was sparked when he was stung by a blue button jelly as a child. He saw what appeared to be multiple jellyfish floating in the bay. However, these jellyfish were unlike anything Sugimoto had seen in his life.

“I remembered all the jellyfish species of Japan from books I’d read, but these were morphologically different from any species I knew,” Sugimoto explains to NOAA.

Having taught himself how to raise jellyfish from books at the local library, Sugimoto took home multiple jellyfish not only to raise them to maturity but also to study them at home. Given his understanding of jellyfish, Sugimoto was surprised by the appearance of the jellyfish as they matured. The jellyfish began to form gonads that Sugimoto had not seen in any of the books he had read about jellyfish. Consequently, Sugimoto contacted one of the “world’s leading jellyfish experts,” Dr. Allen Collins, to see if he had indeed discovered a new species of jellyfish.

“When Ryoya first contacted me, I didn’t expect this to be something new, but I was excited to work with someone young and passionate,” Collins explains to NOAA. “This was also a great opportunity to obtain some well-preserved specimens and document the genetics and characteristics of an organism from another part of the world.”

Thanks to the research Sugimoto had done with the jellies, he had specimens to provide Collins with, who was able to determine that a new species had been discovered. However, what Sugimoto found was not a true jellyfish; it was something else entirely.

The Integral Jellyfish Is Not a”True” Jellyfish

Once Collins had received the specimens of jellyfish that Sugimoto had raised, he immediately realized that what he had in front of him was not a “true” jellyfish. The jellyfish-looking creature was instead a hydrozoan. On the surface, jellyfish and hydrozoans look similar. However, there is a significant difference between the two: true jellyfish belong to a specific group, while hydrozoans comprise multiple species.

The integral jellyfish (Orchistoma integrale), named for its gonads that resemble the mathematical symbol for integrals, is a colonial organism composed of multiple individuals. The integral jellyfish, according to the February 2025 study published in the journal Plankton and Benthos Research, is made up of “prominently curled gonads,” an “irregular number of tentacles,” and “many frilly lips.” In contrast, other hydrozoans generally have no lips or very simple ones. Additionally, the integral jellyfish has a “bell-shaped” peduncle, or the fuzzy part of the creature that floats beyond where the tentacles hang.

Understanding how the integral jellyfish developed was only possible thanks to Sugimoto’s self-training in raising the creatures from polyps to adulthood. When he gathered the “pen tip” sized hydrozoans, Sugimoto’s skills kept the jellyfish not only alive but also helped them thrive. Had Sugimoto not known how to do this, not nearly as much about the life cycle of this new species of hydrozoan would be known to date. Nor would there be as many specimens to study, unlocking more understanding into how diverse the world of the more than 3,700 hydrozoans truly is.

Is the Integral Jellyfish Dangerous?

Like other hydrozoans, which include the Portuguese man-of-war, the integral jellyfish is capable of stinging with its tentacles. While people who come into contact with the Portuguese man-of-war receive painful welts from the venom, it is not yet clear what danger, if any, the integral jellyfish poses to people.

It is known that the tentacles of the integral jellyfish have enough venom to kill shrimp. However, there are no reports of the integral jellyfish stinging people to date. It is also not clear if the integral jellyfish has ever stung anyone prior to being named a new species. While Sugimoto spent several years raising and studying the integral jellyfish, there is no information regarding how much venom is in their tentacles. Consequently, it still needs to be determined how dangerous, if at all, integral jellyfish are to people.

Unanswered Questions About the Integral Jellyfish

Although much is known about the integral jellyfish, many questions about this marine creature remain unanswered. Currently, what is known is the structure of the jellyfish, the fact that they reside in shallow waters, and that they belong to a family of hydrozoans found worldwide. However, that is where our current knowledge ends, at least as of the study published earlier this year. There is far more that needs to be learned about the integral jellyfish, including what it eats and, more importantly, according to Collins, why the species was located for the first time in the northwest portion of the Pacific Ocean.

“The integral jellyfish belongs to an order of organisms that’s pretty ubiquitous. You can find organisms from this group almost anywhere you go,” Collins states to NOAA. “But this discovery is surprising in the sense that we’ve never seen a species from this family in the northwest Pacific Ocean.”

Sugimoto has questions of his own, including whether the integral jelly has always been in Japan but was just never seen, whether the jellyfish migrated from another area and Sugimoto was just lucky enough to be the first to find them, as well as if they accidentally got transported in by another means altogether. For now, both Sugimoto and Collins will continue on with their work with the integral jellyfish to learn all there is to know about the creature that may help with the understanding of hydrozoans discovered in the future as well.