Australia has a seriously strange entry in its enormous list of creatures that could kill you. Two new species of jellyfish have been discovered, one of which appears to defy everything we know about the invertebrates. The other is just really, really dangerous.

Until now Irukandji were thought to be fourteen species of very small jellyfish. While their sting is initially moderately painful, they are best known for the horrific pain that occurs about half an hour later. Although only occasionally fatal, the pain is so great there is speculation some people have deliberately drowned themselves afterward as the only way to stop the agony.

While they have been found in coastal waters around the world, most sightings (and stings) have been off the north coast of Australia. They are unique in having stingers on their bell, as well as on their tentacles, and can fire stingers at nearby creatures, causing pain without direct contact.

Dr Lisa-Ann Gershwin of CSIRO Marine and Atmospheric Research has described two new Irukandji species. Malo bella is similar to, albeit smaller than, one of the previously known species, M. maxima. Keesingia gigas, on the other hand is something truly new. For a start it is much larger than any Irukandji ever seen, 50cm long rather than a few millimeters. It also has characteristics each of which were thought to be limited to different families of Cnidaria. 

The strangest aspect, however, is that it appears to have no tentacles. Although only one specimen has been collected, photographs of two others in the wild appear to be from the same species. "Jellyfish always have tentacles ... that's how they catch their food," Gershwin told Australian Geographic. "The tentacles are where they concentrate their stinging cells."

In announcing the discovery Girshwin writes, “Whether it is a feature of the species that they are so fine as to be overlooked, or that they are genuinely lacking, or that it is mere coincidence that they have been broken off in all three, is unclear.” 

Gershwin has recently produced methodology for predicting when more common Irukandji jellyfish pose a threat, and hopes that further study of these species will allow the same results. With K gigas having been caught off the popular tourism spot of Shark Bay, she will not be the only one.