A rediscovered species of tropical octopus displays social interactions and mating behavior unlike that of any other species of the many-armed sea creatures, researchers say.

The species, the larger Pacific striped octopus, is among the most social ever seen, they say; whereas most octopus species are strictly solitary, the Pacific striped variety are often found off the Pacific coasts of Nicaragua and Panama in social groups of as many as 40 animals.

They have their own preferred method of mating as well: while most species find the males sharing sperm with females at a distance for a quick escape should be females become aggressive — or hungry in a cannibalistic way — mating pairs of the striped species seem happy to share cavities in a reef for at least a few days while mating.

They've even been seen sharing meals in a beak-to-beak position not observed in the 300 or so other species, researchers report in the journal PLOS ONE.

These unique behaviors mark that the larger Pacific striped octopus "are one of the most mysterious and captivating species," says Rich Ross, a senior biologist at the California Academy of Sciences.

"It's the most amazing octopus that I've ever gotten to work with," he adds.

It was originally discovered off the coast of Panama nearly 40 years ago, but most scientists did not believe it was a separate species from already known specimens.

The small octopus — despite the "larger" in its name is not much larger than a tennis ball — has not been classified as a unique species.

Additionally, as if its social and mating habits weren't odd enough, it has displayed one more unique behavior, seen when it's hunting prey.

While most species go after prey with all eight of their arms, the Pacific striped octopus will stalk its favorite prey, shrimp, gently extend one arm — well, tentacle — to gently tap the shrimp to startle it into running directly into the rest of its arms.

"I've never seen anything like it," says marine biologist Roy Caldwell from the University of California, Berkeley. "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 animal's behavior, so different from other octopus species, shows how much is yet unknown about the many-armed creatures, Ross says.

"It reminds us how much we still have to learn about the mysterious world of cephalopods."

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