A huge new species of jellyfish discovered off western Australia looks a bit like a plastic bag—but one that can deliver a potentially lethal sting. Keesingia gigas is as long as a human arm, though bizarrely, none of the specimens caught or photographed appear to have any tentacles, the Guardian reports. But "jellyfish always have tentacles ... that's how they catch their food," says the researcher who discovered the species. "The tentacles are where they concentrate their stinging cells," she explains, suggesting the new species may have tentacles, but by "random chance" the specimens obtained don't have them any longer.
Even without tentacles, the new species is "an absolute whopper of a jellyfish," the researcher tells Australia's ABC News. The jellyfish belongs to a group known as Irukandji jellyfish, which have a sting that causes extreme pain, vomiting, and sometimes heart failure or stroke. Most Irukandji jellyfish are only around the size of a fingernail, and it's not clear whether the new species' bigger size equals a bigger sting. "There doesn't appear to be a direct link between size and toxicity," the researcher says. (Bad news for swimmers: The jellyfish population is booming.)