Many deep-sea squid actively grab their prey, sporting two muscular tentacles used to drag unsuspecting prey into their mouths.
But one squid species that lives down deep—the "wimp" of the proverbial playground—has limp noodles for arms. Scientists have wondered for years how it managed to catch and eat anything.
Grimalditeuthis bonplandi also lacks the hooks, suckers, sticky pads, or glowing spots—called photophores—present on the tentacle tips or clubs of their more muscular brethren. These elaborate clubs help squid lure or hang on to meals.
Now, new underwater video suggests that G. bonplandi wiggle their bare clubs to draw in animals like crustaceans and fish. The wriggling either sets off bioluminescence—which many deep-sea organisms flock to like moths to a flame—in the water or mimics the vibrations given off by swimming worms or shrimp, would-be prey for the crustaceans and fish.
But rather than getting dinner, these curious animals find themselves on the menu. (See more pictures of squid.)
Grimalditeuthis bonplandi is strange because it's the only known squid with bare clubs and because it likely uses movement to bring in a meal, said Henk-Jan Hoving, a marine biologist at the Helmholtz Centre for Ocean Research in Kiel, Germany, and lead author of a new study on the squid.
"This is [also] the only squid we know of that have feeding tentacles that can't shoot out," and grab prey like most other squid, said study co-author Bruce Robison, a deep-sea ecologist with the Monterey Bay Aquarium Research Institute (MBARI).
Closer examination of G. bonplandi tentacles showed a distinct lack of musculature compared to the tentacles of closely related species, according to the study, published August 27 in the journal Proceedings of the Royal Society B.
Robison speculates that the squid shoots its entire body forward to capture prey lured in by its bare tentacle clubs, rather than using its tentacles to bring its meal toward the mouth.
"When you go fishing, you like to have really thin fishing line," Robison said. "If we view this as a lure at the end of a fishing line, having a really slender thread out to your bait makes sense."
Watch video footage of this rare squid.
Although scientists have known about G. bonplandi since 1839, specimens with intact tentacles weren't described until the late 1990s. The skinny, delicate tentacles were easily ripped off when the animals got tumbled around in net tows.
So it wasn't until a researcher dug one out of the stomach of a lancetfish (Alepisaurus ferox) that scientists could definitively attribute these wimpy limbs to G. bonplandi, said study co-author Stephanie Bush, a marine ecologist at Smithsonian's National Museum of Natural History in Washington, D.C.
But researchers had never seen it alive until a September 2005 trip into the depths of the Monterey Submarine Canyon (map), when MBARI snagged the first video footage of this animal.
It was pure chance that the research team stumbled on this rare squid.
"MBARI at least had never seen this animal before," said Bush. "And we have never seen it since."
That may be in part because central California is a little out of this squid's range—they're probably seen more frequently in southern California, Bush said. (Related:"Vampire Squid Turns 'Inside Out.'")
When the research team started to write up their results, they soon learned that remotely operated vehicles working on oil rigs in the Gulf of Mexico had gotten footage of six more G. bonplandi between 2008 and 2010. They decided to roll those observations together with the Monterey footage in their analysis.
Much of deep-sea work tends to be opportunistic, added MBARI's Robison. Animal distributions are patchy in the deep, so researchers take what they can get when they get it. But it also means that never before or rarely seen organisms could pop up at any moment. (Related: "Monster Glowing Squid Caught on Camera.")
"We've been doing this for 24 years and we're still finding new animals and new behaviors," he said.
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