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Deep sea squid lure prey for attack

Master of trickery Deception occurs even in the deepest parts of oceans, as scientists have just discovered that a deep-sea squid pretends to be a small animal before making a deadly attack.

The secret weapon turns out to be a long fishing line-type appendage with a club at the end that the squid waves around like a hand puppet, fooling passersby.

"These tentacle club movements superficially resemble the movements of small marine organisms," according to Hendrik Hoving, a researcher at the Monterey Bay Aquarium Research Institute, and his team.

Their paper, published in the latest issue of the Proceedings of the Royal Society B, describes the first ever observations of the squid Grimalditeuthis bonplandi, in its Atlantic and North Pacific habitats. Remotely operated vehicles (ROVs) permitted observation of the squid and other creatures up to nearly 4 kilometres below the ocean surfaces.

Scientists had been puzzled about this particular squid. The tentacles and clubs of most squid bear suckers and hooks for catching prey. Most of us have seen B-movies where some enormous squid grabs an unaware diver with these tentacles and gobbles him to bits.

The long elastic stalk of G. bonplandi is instead surprisingly "thin and fragile," with no such grabbing devices on it. Now we know why.

The ROVs caught the squid in the act of deception.

Fish-like club

First, the squid deploys its tentacle club far away from the main part of its body. This club is covered in pigment-containing cells known as chromatophores, which create an optical illusion, permitting squid to dramatically change their skin colour and texture. Protective membranes on the club that can flap, giving the club its own propulsion.

"These undulatory and flapping movements of the tentacle clubs superficially resemble the swimming of a small mid-water animal (e.g. worm, fish, squid, shrimp)," the authors write. "We hypothesise that G. bonplandi exploits this resemblance, using the tentacle clubs to attract potential prey towards the squid. How prey is subsequently engulfed by the arms and handled by the suckers remains subject to speculation."

Possible prey animals are smaller squid, octopi, shellfish, and other species that might go after small animals like worms and shrimp. Even if these victims cannot see the fake "shrimp," they can sense the vibrations created by the flapping movement.

It's clearly challenging to study animal activities that take place so deep in the ocean, but the researchers think it's possible that other squid species and marine molluscs also use deceptive lures to catch their dinners.