A box jellyfish is a killer without peer

One touch of venom: a box jellyfish is a killer without peer

Jamie Seymour

Found in the waters off northern Australia, the box jellyfish Chironex fleckeri is not the only marine invertebrate to use venom, but it is the possessor of arguably the most lethal venom in the world. In the past half century, sixty-five Australians have been killed by it. C. fleckeri’s body (or bell) can grow to a foot wide and can support as many as sixty tentacles, each more than seven feet long, each capable of delivering a fatal touch. Since 1995 I’ve been studying why and how this jellyfish uses such high-octane venom.

Most jellies feed on plankton. But once C. fleckeri’s bell reaches a diameter of four inches, this jelly begins to feed on fish. Its venom seems tailor-made for attacking the nervous and cardiac systems of vertebrates: when C. fleckeri selects prey, it can sign their death warrant with a single flick of a tentacle, whose every inch contains 2.5 million stinging nematocysts–specialized cells that are ripe with venom.

C. fleckeri, unlike the typical jellyfish, is a fine swimmer. Some individuals have been clocked at speeds of up to two and a half knots–useful if you want to pursue fish. Having nabbed its prey, the box jellyfish moves the captive to its stomach for predigestion. Surprisingly, however, the absorption of organic matter does not take place there. Instead, the semidigested broth is directed to canals lining the interior walls of each tentacle, where nutrient uptake then occurs. Why this process in C. fleckeri (and most other box jellies) but not in other species of jellyfish? The answer lies in its high energy demands: its metabolic rate is ten times greater than that of other jellyfishes. The standard jellyfish stomach is a simple, pouchlike affair. That’s fine if your principal food is plankton, but not much use if you’re trying to feed on fish. The canals inside C. fleckeri’s tentacles (which bear an uncanny resemblance to the villi that line vertebrate digestive systems) dramatically increase the internal surface area of the tentacles, allowing more organic matter to be absorbed in less time than would be possible with a conventional jellyfish digestive system.

In the world of jellyfish, C. fleckeri–fast on its tentacles, furious with its venom–is in a league of its own.

As for why he devotes so much time to the lethal box jellyfish, Jamie Seymour (“One Touch of Venom,” page 72) says, “Why wouldn’t you want to work on an animal that’s 96 percent water, doesn’t have a brain as such but can use visual images, swims at high speeds, and causes death in minutes?” Seymour, left, is a senior lecturer in the School of Tropical Biology at James Cook University in Queensland, Australia. His major area of research is the seasonal variations in populations of box jellies, other cnidarians, and tropical insects. He is also director of an organization that links and publicizes medical and biological research on the box jellyfish. Photographer Paul A. Sutherland learned to snorkel at the age of four in Saudi Arabia, where his father was a U.S. foreign service officer. After attending college in the United States, Sutherland returned to the Middle East and worked in the oil fields there for six years. A full-time photographer since 1996 (www. sutherlandimages.com), he specializes in the underwater world and has made more than 2,500 dives. “Every time I get in the water,” he says, “the rest of the world ceases to exist.”

COPYRIGHT 2002 American Museum of Natural History

COPYRIGHT 2003 Gale Group