Pacific striped octopus displays 'incredibly unique' hunting behaviour
Hunting for food is a pantomime for a species of octopus that reaches out and taps its prey on the shoulder.
The tropical cephalopod may not utter the words "behind you" but startles the victim so much it becomes lunch.
Professor Roy Caldwell, from the University of California at Berkeley, who led a team studying the larger Pacific striped octopus in captivity, said: "I've never seen anything like it. Octopuses typically pounce on their prey or poke around in holes until they find something.
"When this octopus sees a shrimp at a distance, it compresses itself and creeps up, extends an arm up and over the shrimp, touches it on the far side and either catches it or scares it into its other arms."
The octopus also displays other unusual kinds of behaviour, the scientists revealed.
While most octopuses are solitary creatures, the larger Pacific striped has been seen in groups of up to 40 off the coasts of Nicaragua and Panama.
It also has peculiar mating habits, for an octopus. Male octopuses typically mate at arm's length, getting ready to flee if the female becomes too aggressive or hungry.
But the sex life of the larger Pacific striped is a lot cosier. The researchers observed mating pairs engaging sucker-to-sucker and beak-to-beak, as if kissing. Couples also co-habited in the same den and even got within beaking distance of one another to share meals.
In addition females mated often and laid eggs over several months, while most female octopuses die after a single brood.
The animals also appeared to communicate with striking displays of coloured patterns.
"They certainly respond to one another when they display their highly contrasting stripes and spots, so their colouration appears to be useful for group living," said Prof Caldwell.
The larger Pacific striped octopus lives in discarded shells or rock cavities at the mouths of rivers.
Co-author Dr Richard Ross, from the California Academy of Sciences, said: "Personally observing and recording the incredibly unique cohabitation, hunting and mating behaviours of this fascinating octopus was beyond exciting.
"It reminds us how much we still have to learn about the mysterious world of cephalopods."
The research is reported in the online journal Public Library of Science ONE.