A new species does not always emerge from an unexplored corner of the ocean. Sometimes it has been in front of scientists all along, hiding behind a familiar name. Researchers studying box jellyfish near Singapore have identified one such case: a highly venomous species previously mistaken for another jellyfish, now described as Chironex blakangmati.

The newly described species was found in specimens collected from Singapore beaches in 2020 and 2021. Scientists initially identified the animals as Chironex yamaguchii, a box jellyfish first discovered in Okinawa, Japan. A closer look at both their bodies and DNA revealed the Singapore jellyfish was a species of its own.

How scientists told them apart

The two species look remarkably similar, which made the mix-up understandable – but researchers found a key physical difference. Chironex blakangmati lacks certain branched canal structures at the bottom of its bell-shaped body that are found in C. yamaguchii and other known Chironex species. These structures sit within parts of the jellyfish called perradial lappets, which reinforce the muscles involved in swimming. Genetic differences provided further evidence that the Singapore specimens belonged to a separate species. Study co-author Cheryl Ames, a professor of applied marine biology at Tohoku University in Japan and a research associate at the Smithsonian National Museum of Natural History, said the two look remarkably alike but turned out to be completely distinct. The team even re-examined an old sample of C. yamaguchii that Ames had kept from her earlier work in Okinawa to make the comparison.

A dangerous and poorly mapped group

The new species belongs to the Chironex genus, whose members are known for powerful venom. Their tentacles contain specialised stinging cells called nematocysts that inject venom on contact with prey or people, and some Chironex species can deliver stings severe enough to kill humans. Box jellyfish are also more active swimmers than many expect: rather than drifting with currents, they use strong muscles and complex eyes to navigate and pursue prey. That makes mapping their distribution important. The team made another surprise discovery while examining Singapore’s box jellyfish: they found Chironex indrasaksajiae, the Thai sea wasp, in Singaporean waters. Previously known from waters around Thailand, its presence in Singapore marks a range expansion. Scientists still know relatively little about box jellyfish distribution across the region, and identifying where species occur could help researchers better assess the risks they pose to swimmers. Box jellyfish stings are estimated to cause around 40 deaths globally each year, though researchers suspect the true number could be considerably higher.