By Rachel A. Becker, National Geographic

The octopuses nonchalantly sidle up next to each other, circling but not getting too close.

Then, in a sudden tangle of arms, the two larger Pacific striped octopuses go at it, bodies heaving. But the weird thing is, these amorous cephalopods are mating face to face.

“The beak-to-beak mating is just crazy nutty,” says Richard Ross , senior biologist at the Steinhart Aquarium in the California Academy of Sciences and co-author of a new study on the species.

“No one else does anything else like that.” (Also see " Fighting Octopuses Video Is First to Show How They 'Talk .'")

All other known octopus species mate either by the male mounting the female or inserting his mating arm into her from a distance.

View Images A small male larger Pacific striped octopus stalks its prey. Photograph by Roy L. Caldwell

Face-to-face mating is just one of the bizarre behaviors unearthed in the first published study of the larger Pacific striped octopus, tennis ball-size creatures that live on the muddy seafloor of the Eastern Pacific.

The research, which appears August 12 in the journal Public Library of Science One , revealed phenomena never before seen in octopuses, including males and females sharing the same den and tapping prey on the "shoulder" to startle it into waiting arms.

Strange But True

Hints of this paper have been teasing cephalopod lovers and the scientific community for over a year , but rumors that these octopuses might be very different from their fellow species has been around—and disbelieved—since the larger Pacific striped octopus first popped up in a scientific illustration in 1977.

In the 1980s and 1990s, Panamanian scientist Arcadio Rodaniche reported seeing the octopuses in colonies of up to 40 individuals, as well as other odd behaviors such as denning together.

Octopuses are notoriously solitary cannibals, so the idea they would not only form colonies but cohabit in the same den was too crazy for the scientific community to handle. Rodaniche's manuscript remained unpublished. (See "Journey of Octopus Discovery Reveals Them to Be Playful, Curious, Smart.")

Now, 25 years later, Rodaniche has been vindicated—and as one of the co-authors of the study, his observations have finally been published.

“I was beginning to doubt my data was any good,” Rodaniche says. “It’s been a very pleasing surprise to be able to see my data being published after all these years.”

Lovers Not Fighters

For two years, the study team observed 24 larger Pacific striped octopuses acquired from commercial aquarium wholesalers.

Because the researchers feared the animals might eat each other, they kept them physically separated but still able to see and communicate with each other. The team then paired them up in various male/female combinations in controlled circumstances.

The scientists couldn't confirm that the octopuses form colonies, but they did see one male and female couple sharing the PVC pipe "den," mating daily and sharing food. Caldwell speculates the animals might shack up because there aren't many dens available in their ocean habitat.

Other octopus species aren't quite so into cuddling, says Janet Voight , a cephalopod biologist at Chicago's Field Museum of Natural History who was not involved in the new study.

Their attitude usually is, "I have some of your sperm, I’ve had enough. I’ll kill you—and eat you, of course," she says.

As a way to avoid getting eaten during mating, many male octopuses insert a specialized arm that shoots spermatophores into the female's mantle, an organ-filled structure behind its head. The other preferred position is the male mounting the female. Never have scientists observed beak-to-beak octopus sex.

The face-to-face position might be linked to the females' unusual reproduction.

Most octopus species lay eggs in a single clutch and then die once the young hatch, but larger Pacific striped females lay egg clutches throughout their reproductive lifetimes.

So face-to-face mating may have evolved to give the males access to females tucked away in their dens protecting their eggs. (Also see " Longest-Living Octopus Found, Guards Eggs for Record 4.5 Years .")

Voight adds that the study does exactly what it set out to do: Report on the octopus species’ behavior. In fact, Voight was hungry for more details about the animal, she says.

Skilled Hunters

While they might be cuddlier and more social than most octopuses, larger Pacific striped octopuses are relentless hunters.

"They actually stalk their prey," says study leader Roy Caldwell , a biologist at the University of California, Berkeley. "That's something you don't see in other octopus."

After creeping up on an unsuspecting shrimp, for example, an octopus will tap the creature on its tail end, frightening it straight into the predator's waiting arms, the team's observations showed.

WATCH: Scientists studying several larger Pacific striped octopuses have observed some remarkable unique behavior—including the way they sometimes catch prey. Video courtesy Roy Caldwell, University of California, Berkeley.

"It's like tapping someone on the wrong shoulder and having them jump into you," Caldwell says.

Observing larger Pacific striped octopus behavior in captivity is a huge step toward understanding these octopuses that break the mold.

But it still doesn't tell us how these behaviors might help an octopus survive in its native habitat. “You’ve got wonder how they’re living in nature,” Voight says. ( Watch video: "Stealthy Octopus Leaps From Water and Attacks Crab .")

To that end, the study authors plan to observe the species in the wild.

Study leader Caldwell adds the more we learn about octopuses in general, the less weird these larger Pacific striped octopuses will seem.