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Brainless Jellyfish Actively Hunt, Surprise Experts

Jun 06, 2015 11:05 AM EDT
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For most, jellyfish have always been those overly alien things that float in aquariums and across our television screens during brief stints of self-education. Ah, a jellyfish! Look how it... is weird. For most, that's about as far as they can go when describing these creatures. They're not "clever," or "scary" or "wild." In fact, some are even mistaken for drifting plants, barely moving as the currents dictate where they head. However, researchers have now identified one group of jellies that actively lure and capture prey - a revelation that soundly disproves assumptions that these creatures lead a mindless existence.

"They're not opportunistically grazing - they're deliberately fishing," researcher Robert Courtney, or James Cook University, said in a statement. "They're targeting and catching fish that are at times as big as they are, and are far more complex animals. This is a really neat animal that is displaying a surprisingly complex prey capture strategy."

Courtney and his colleagues reportedly spent a great deal of time studying the Irukandji box jellyfish (Carukia barnes - not pictured) in an effort that was originally aimed towards better understanding their deadly paralytic toxin.*

It was first thought that especially with the aid of their deadly strings, C. bames would be a particularly mindless hunter.

"Most jellyfish just swim around or are driven by the currents of the ocean," Courtney explained to ABC News. "They're basically considered an opportunistic grazer [because] anything that runs into the tentacles then gets consumed."

However, after capturing several samples of the creatures and recording them for 24-hour periods, the researcher and his team quickly learned that C. bames actually hunted deliberately, and was not simply a hazard that fish blundered into.

"This species is small, less than two centimeters across the bell, they're 96% water, they lack a defined brain or central nervous system, and yet they're using their tentacles and nematocyst clusters (stingers) like experienced fishers use their lines and lures," Courtney added. (Scroll ro read on...)

According to results published in the journal PLOS One, during the day, the jellyfish are drawn towards patches of water bathed in sunlight. There, they extend their long tentacles and "fish."

"The nematocyst clusters look like a series of bright pearls, which the jellyfish twitches to attract the attention of its prey, like a series of fishing lures," Courtney explained."It's a very deliberate and selective form of prey capture."

Most interestingly, it was clear that these jellies don't simply happen to be twitching the right war, which happens to attract the right prey. Using infrared-sensitive equipment, the researchers determined that in complete dark, C. bames actually retracted their tentacles - bunching the nematocysts until morning.

"We believe they may do this to conserve energy when visually oriented prey (larval fish) may also be less active," researcher and co-author Jamie Seymour added.

"It's a highly successful fishing strategy, and the only account of a box jellyfish using aggressive mimicry to capture prey," Courtney said. Additionally, "this has just given us a little bit more of a handle on what's going on with a venomous animal that we don't really know too much about."

*More about this deadly hunter:

C. bames and a number of other Irukandji (a group of tiny carybdeids) can be found in waters north of Agnes Waters Queensland, the Northern Territory and Western Australia south of Exmouth and are infamously poisonous. In 2002, for instance, these jellies were blamed for the deaths of two unlucky swimmers. Another 120 required hospitalization that year.

Following a sting, beachgoers have reported a burning sensation, followed by muscular pain, headaches and even vomiting. However, these symptoms usually start up 30 to 40 minutes after a sting, allowing most victims to get out of the water and seek medical attention in time.

For more great nature science stories and general news, please visit our sister site, Headlines and Global News (HNGN).

- follow Brian on Twitter @BS_ButNoBS

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